Thông tin tài liệu
EFFECT OF SIZE AND VOLUME FRACTION OF
REINFORCEMENT ON THE PROPERTIES OF LIGHT
METALS
HO KAO FENG CALVIN
(B. Eng.(Hons.), NUS)
A THESIS SUBMITTED
FOR THE DEGREE OF MASTER OF ENGINEERING
DEPARTMENT OF MECHANICAL ENGINEERING
NATIONAL UNIVERSITY OF SINGAPORE
2003
Acknowledgements
The author will like to express his sincere gratitude and appreciation to the
following people:
1. Dr. M. Gupta for his invaluable guidance and supervision.
2. Mr. Thomas, Mr. Maung Aye Thein, Hong Wei, Mr. Khalim, Mr.
Juraimi and Mdm. Zhong X L from the Materials Science Lab for their
technical support and assistance.
3. Mr. Chua Beng Wah, Miss Sharon Nai and Mr. Syed Fida Hassan for
their friendship, encouragement and valuable discussions.
4. All other research scholars for their advice and help given.
5. Mr. Lau P K for his advice and assistance in extrusion.
6. Mr. Chiam and Joe Low from the Experimental Mechanics Lab for his
assistance in tensile testing.
7. Mr. Lam from TSU for his assistance in machining.
8. N. Srikanth for his advice and assistance in dynamic modulus testing.
i
Table of Contents
ACKNOWLEDGEMENTS .................................................................................................................... i
TABLE OF CONTENTS .......................................................................................................................ii
SUMMARY ...............................................................................................................................................vi
LIST OF ILLUSTRATIONS .............................................................................................................viii
CHAPTER 1: INTRODUCTION........................................................................................................ 1
CHAPTER 2: LITERATURE RESEARCH.................................................................................... 4
2.1
PROCESSING M ETHODS..........................................................................................................5
2.1.1
Solid State Processing.................................................................................................... 5
2.1.1.1
Powder Metallurgy .........................................................................................................5
2.1.1.2
Diffusion Bonding..........................................................................................................6
2.1.1.3
Mechanical Alloying......................................................................................................7
2.1.2
Semi-solid Processing..................................................................................................... 7
2.1.3
Liquid State Processing.................................................................................................. 8
2.1.3.1
Dispersion Process.........................................................................................................8
2.1.3.2
Infiltration ......................................................................................................................9
2.1.3.3
Spraying.......................................................................................................................10
2.1.3.4
In-situ Fabrication........................................................................................................10
2.1.4
2.2
New Innovative Method................................................................................................11
TYPES OF REINFORCEMENT ................................................................................................12
2.2.1
Continuous fiber ............................................................................................................12
2.2.2
Metal wires.....................................................................................................................13
2.2.3
Whiskers..........................................................................................................................13
2.2.4
Short fibers .....................................................................................................................13
2.2.5
Particulates.....................................................................................................................14
2.3
THERMOMECHANICAL PROCESSES ....................................................................................15
2.4
INTERFACE CHARACTERISTICS...........................................................................................17
2.5
EFFECT OF REINFORCEMENT SIZE......................................................................................19
2.6
SUMMARY..............................................................................................................................20
ii
CHAPTER 3: MATERIALS AND EXPERIMENTAL PROCEDURES ..............................21
3.1
M ATERIALS............................................................................................................................22
3.2
SYNTHESIS.............................................................................................................................26
3.3
SPECIMEN PREPARATION.....................................................................................................29
3.4
EXTRUSION............................................................................................................................29
3.5
QUANTITATIVE A SSESSMENT OF REINFORCEMENT.........................................................30
3.6
QUANTITATIVE A SSESSMENT OF ALLOYING ELEMENT ..................................................30
3.7
DENSITY M EASUREMENT ....................................................................................................31
3.8
M ICROSTRUCTURE CHARACTERIZATION..........................................................................31
3.9
X-RAY DIFFRACTION STUDIES ...........................................................................................31
3.10
M ECHANICAL TESTING........................................................................................................32
3.10.1
Microhardness Measurement......................................................................................32
3.10.2
Macrohardness Measurement.....................................................................................32
3.10.3
Tensile Testing...............................................................................................................33
3.10.4
Dynamic Elastic Modulus Testing..............................................................................33
3.11
FRACTOGRAPHY....................................................................................................................34
3.12
THERMAL MECHANICAL ANALYSIS ..................................................................................34
CHAPTER 4: RESULTS .....................................................................................................................36
4.1
PHASE I & II RESULTS.........................................................................................................37
4.1.1
Processing.......................................................................................................................37
4.1.2
Density Measurement ...................................................................................................37
4.1.3
Microstructural Characterization..............................................................................38
4.1.4
Mechanical Characterization......................................................................................42
4.1.4.1
Hardness.......................................................................................................................42
4.1.4.2
Tensile Properties.........................................................................................................42
4.1.5
Fractography..................................................................................................................43
4.1.6
Thermal Mechanical Analysis.....................................................................................46
4.2
PHASE III RESULTS...............................................................................................................47
4.2.1
Processing.......................................................................................................................47
4.2.2
Quantitative Assessment of Reinforcement ...............................................................47
iii
4.2.3
Quantitative Assessment of Alloying Element..........................................................48
4.2.4
Density Measurement ...................................................................................................48
4.2.5
Microstructural Characterization..............................................................................49
4.2.6
X-ray Diffraction Results.............................................................................................53
4.2.7
Mechanical Characterization......................................................................................53
4.2.7.1
Hardness.......................................................................................................................53
4.2.7.2
Tensile Properties.........................................................................................................54
4.2.8
Fractography..................................................................................................................54
4.2.9
Thermal Mechanical Analysis.....................................................................................57
4.3
PHASE IV RESULTS..............................................................................................................58
4.3.1
Processing.......................................................................................................................58
4.3.2
Quantitative Assessment of Reinforcement ...............................................................58
4.3.3
Quantitative Assessment of Alloying Element..........................................................59
4.3.4
Density Measurement ...................................................................................................59
4.3.5
Microstructural Characterization..............................................................................60
4.3.6
X-ray Diffraction Results.............................................................................................64
4.3.7
Mechanical Characterization......................................................................................65
4.3.7.1
Hardness.......................................................................................................................65
4.3.7.2
Tensile Properties.........................................................................................................65
4.3.8
Fractography..................................................................................................................66
4.3.9
Thermal Mechanical Analysis.....................................................................................69
CHAPTER 5: DISCUSSIO N ..............................................................................................................70
5.1
PHASE I & II DISCUSSION ....................................................................................................71
5.1.1
Processing.......................................................................................................................71
5.1.2
Secondary processing ...................................................................................................71
5.1.3
Density and Porosity.....................................................................................................72
5.1.4
Microstructure...............................................................................................................72
5.1.5
Mechanical Behavior....................................................................................................73
5.1.6
Fractography..................................................................................................................75
5.1.7
Thermal Mechanical Analysis.....................................................................................75
iv
5.1.8
5.2
Proceeding to Phase III................................................................................................75
PHASE III DISCUSSION .........................................................................................................76
5.2.1
Processing.......................................................................................................................76
5.2.2
Secondary processing ...................................................................................................77
5.2.3
Density.............................................................................................................................77
5.2.4
Microstructure...............................................................................................................78
5.2.5
Mechanical Behavior....................................................................................................80
5.2.6
Fractography..................................................................................................................82
5.2.7
Coefficient of Thermal Expansion (CTE)..................................................................82
5.2.8
Proceeding to Phase IV................................................................................................83
5.3
PHASE IV DISCUSSION.........................................................................................................84
5.3.1
Processing.......................................................................................................................84
5.3.2
Secondary Processing...................................................................................................84
5.3.3
Density.............................................................................................................................85
5.3.4
Microstructure...............................................................................................................85
5.3.5
Mechanical Behavior....................................................................................................87
5.3.6
Fractography..................................................................................................................90
5.3.7
Coefficient of Thermal Expansion (CTE)..................................................................90
CHAPTER 6: CONCLUSIONS .........................................................................................................91
CHAPTER 7: RECOMMENDATIONS..........................................................................................96
REFERENCES………………………………………………………………………………..98
APPENDICES ………………………………………………………………………………. 103
v
Summary
This study addresses the feasibility of synthesizing nanometric alumina
reinforced aluminium composites using the innovative disintegrated melt deposition
(DMD) technique and the effect of reinforcement size and volume fraction on the
microstructural and mechanical properties of aluminium.
In this study, pure aluminium material was fabricated in the Material Science
Laboratory of National University of Singapore (NUS). The material was successfully
synthesized using DMD technique followed by extrusion at different extrusion
temperatures (Phase I) and extrusion ratios (Phase II). The effect of different secondary
processing parameters on the microstructure and mechanical properties was
investigated to obtain optimum parameters for the subsequent processing of
aluminium-based composites.
Varying amounts of magnesium were added to the aluminium matrix to
investigate the wettability of nanometric (0.05µm) alumina particulates in Al-Mg
(Phase III). An attempt was made to correlate the magnesium content of the matrix to
the alumina incorporation and, microstructural and mechanical properties of the
composite. An optimum magnesium content was chosen for the matrix of composites
in the subsequent phase. Alumina particulates in the sizes of 0.3 µm, 1 µm and 10µm
were added to an Al-Mg matrix to investigate the effect of different reinforcement size
on the microstructural and mechanical properties of Al-Mg (Phase IV).
The first 2 phases of the study verified the effect of extrusion parameters on the
grain size of the matrix. Generally, grain size refinement was found to occur when the
extrusion temperature is reduced or the extrusion ratio is increased. Grain size
refinement subsequently led to an increase in hardness, 0.2% yield stress (YS),
ultimate tensile stress (UTS) and a decrease in ductility. The elastic modulus and
vi
coefficient of thermal expansion (CTE) was insensitive to changes in extrusion
parameters. Phases I & II revealed that the optimal extrusion temperature and ratio was
25°C and 26.45:1 respectively.
Phase III demonstrated the feasibility of fabricating nanometric alumina
reinforced aluminium composites when sufficient magnesium is added to the
aluminium matrix as a wetting agent. Alumina incorporation increased with higher
magnesium content in the matrix. The maximum volume fraction of nanometric
alumina was low but the presence of small volume fraction of uniformly distributed
nanometric reinforcement was sufficient to bring about a significant improvement in
mechanical properties. Phase III revealed that the addition of 5 wt.% magnesium to
aluminium holds the promise to realize the best mechanical properties.
Phase IV showed that larger alumina particulates are easier to incorporate in an
Al-Mg matrix. However, the larger sized particulates tended to form clusters. This
resulted in higher porosity and hence a reduction in mechanical properties. As a result,
properties such as hardness, elastic modulus, 0.2% YS and UTS decreased with
increasing reinforcement size. An improvement in ductility was observed as
reinforcement size decreased, until a threshold size of 0.3µm.
The results obtained in the present study revealed that a small addition of
nanometric alumina reinforcement has great potential in significantly enhancing the
mechanical properties of aluminium.
vii
List of Illustrations
FIGURE 3-1
FLOW CHART SHOWING THE OVERVIEW OF THE PROJECT .
24
FIGURE 3-2
RAW MATERIALS USED: A LUMINIUM GRANULES, MAGNESIUM TURNINGS AND ALUMINA.
25
FIGURE 3-3
SCHEMATIC DIAGRAM OF THE EXPERIMENTAL SET -UP FOR THE DMD CASTING.
26
FIGURE 3-4
RESISTANCE FURNACE USED FOR DMD.
27
FIGURE 3-5
COMPONENTS OF MOLD AND METALLIC SUBSTRATE.
28
FIGURE 3-6
TOOLS USED IN FABRICATION (FROM BACK): GRAPHITE CRUCIBLE FITTED WITH
NOZZLE /PLUG AND MILD STEEL LID, CERAMIC TUBE , MILD STEEL STIRRER,
THERMOCOUPLE.
29
FIGURE 4-1
REPRESENTATIVE SEM MICROGRAPHS SHOWING GRAIN MORPHOLOGY OF AL
EXTRUDED WITH AN EXT RUSION RATIO OF 20.25:1 AND TEMPERATURE OF: (A) 25°C, (B )
85°C, (C ) 150°C, (D) 250°C AND (E) 350°C.
40
FIGURE 4-2
REPRESENTATIVE SEM MICROGRAPHS SHOWING GRAIN MORPHOLOGY OF AL
EXTRUDED AT 85°C WITH AN EXTRUSION RATIO OF: (A) 26.45:1 AND (B)12.96:1.
41
FIGURE 4-3
REPRESENTATIVE SEM MICROGRAPHS SHOWING THE FRACTURE SURFACE OF AL
EXTRUDED WITH AN EXTRUSION RATIO OF 20.25:1 AND TEMPERATURE OF: (A) 25°C, (B )
85°C, (C ) 150°C, (D) 250°C AND (E) 350°C.
44
FIGURE 4-4
REPRESENTATIVE SEM MICROGRAPHS SHOWING THE FRACTURE SURFACE OF AL
EXTRUDED AT 85°C WITH AN EXTRUSION RATIO OF: (A) 26.45:1 AND (B) 12.96:1.
45
REPRESENTATIVE SEM MICROGRAPHS SHOWING GRAIN MORPHOLOGY OF: (A) A L1.6M G/A L2 O3 , (B) A L-2.9M G/A L2 O3 AND (C) AL-3.4M G/A L2 O3 .
50
FIGURE 4-5
FIGURE 4-6
REPRESENTATIVE SEM MICROGRAPHS SHOWING UNIFORM DISTRIBUTION OF
INTERMETALLIC AL12 M G17 (INDICATED BY ARROWS) IN: (A) A L-1.6M G/A L2 O3 , (B) A L2.9M G/A L2 O3 AND (C) A L-3.4M G/A L2 O3 .
51
FIGURE 4-7
REPRESENTATIVE FESEM MICROGRAPHS SHOWING DISTRIBUTION OF ALUMINA IN: (A)
A L-1.6M G/A L2 O3 , (B) A L-2.9M G/A L2 O3 AND (C) A L-3.4M G/A L2 O3 .
52
FIGURE 4-8
REPRESENTATIVE SEM MICROGRAPHS SHOWING THE FRACTURE SURFACE OF: (A) A L1.6M G/A L2 O3 , (B) A L-2.9M G/A L2 O3 AND (C) AL-3.4M G/A L2 O3 .
55
FIGURE 4-9
REPRESENTATIVE SEM MICROGRAPHS AT HIGH MAGNIFICATION SHOWING THE
DEFORMATION CHARACTERISTICS OF: (A) A L-1.6M G/A L2 O3 , (B) A L-2.9M G/A L2 O3 AND
(C) A L-3.4M G/A L2 O3 .
56
FIGURE 4-10
REPRESENTATIVE SEM MICROGRAPHS SHOWING GRAIN MORPHOLOGY OF: (A) A L-M G,
(B) A L-M G-0.3µM A L2 O3 , (C) A L-M G-1µM A L2 O3 AND (D) AL-M G-10µM A L2 O3
SAMPLES.
61
FIGURE 4-11
REPRESENTATIVE SEM MICROGRAPHS SHOWING UNIFORM DISTRIBUTION OF
INTERMETALLIC AL12 M G17 (INDICATED BY ARROWS) IN: (A) A L-M G, (B) A L-M G-0.3µM
A L2 O3 , (C) A L-M G-1µM A L2 O3 AND (D) A L-M G-10µM A L2 O3 SAMPLES.
62
FIGURE 4-12
REPRESENTATIVE SEM MICROGRAPHS SHOWING DISTRIBUTION OF ALUMINA IN : (A) A LM G-0.3µM A L2 O3 , (B) A L-M G-1µM A L2 O3 AND (C) A L-M G-10µM A L2 O3 SAMPLES. 63
FIGURE 4-13
REPRESENTATIVE SEM MICROGRAPH SHOWING ALUMINA CLUSTER AND GOOD
INTERFACIAL INTEGRIT Y BETWEEN INDIVIDUAL AL2 O3 PARTICULATES AND MATRIX IN
THE CASE OF A L-M G-10µM A L2 O3 .
64
FIGURE 4-14
REPRESENTATIVE SEM MICROGRAPHS SHOWING THE FRACTURE SURFACE OF: (A) A LM G, (B ) A L-M G-0.3µM A L2 O3 , (C) A L-M G-1µM A L2 O3 AND (D) A L-M G-10µM A L2 O3
SAMPLES.
67
viii
FIGURE 4-15
REPRESENTATIVE SEM MICROGRAPHS AT HIGH MAGNIFICATION SHOWING THE
DEFORMATION CHARACTERISTICS OF: (A) A L-M G, (B) A L-M G-0.3µM A L2 O3 , (C) A LM G-1µM A L2 O3 AND (D) A L-M G-10µM A L2 O3 SAMPLES.
68
FIGURE 5-1
GRAPH OF EXTRUSION LOAD VS. CUMULATIVE MAGNESIUM AND ALUMINA
REINFORCEMENT WEIGHT PERCENT .
77
GRAPH OF 0.2% YS VS. CUMULATIVE MAGNESIUM AND ALUMINA REINFORCEMENT
WEIGHT PERCENT .
81
FIGURE 5-2
FIGURE 5-3
GRAPH OF UTS VS. CUMULATIVE MAGNESIUM AND ALUMINA REINFORCEMENT WEIGHT
PERCENT .
82
FIGURE 5-4
GRAPH OF 0.2% YS, UTS AND DUCTILITY VS. ALUMINA PARTICULATE SIZE.
88
FIGURE 5-5
BAR CHART SHOWING A SUMMARY OF MECHANICAL PROPERTIES OF MATERIALS
FABRICATED IN THE PRESENT STUDY.
89
ix
Chapter 1: Introduction
Chapter 1
Introduction
Metal-matrix composites (MMCs) combine the metallic properties such as
ductility, toughness and environmental resistance with the ceramic properties such as
high strength and high modulus. They offer several advantages in applications where
high strength, high modulus and good thermal conductivities are desirable. One of the
main advantages of MMCs is the ability to tailor the composite behavior for the
intended application. Aluminium-based MMCs reinforced with particulate ceramics
have attracted the interest of many researchers recently owing to their low density,
wide alloy range, heat treatment capability, processing flexibility and low cost.
Particulates such as SiC, Al2O3, TiC, B4C and TiB2 have commonly been used
to reinforce aluminium alloys. The size of the ceramic particulates in commercial
MMCs generally ranges from a few micrometers to several hundred micrometers.
Several studies have indicated that the strengths of particulate composites tend to
increase with decreasing particle size [1]. However, little work has been reported in
open literature concerning the properties of aluminium-based MMCs reinforced with
nanometric particulates. Most of the work involving the use of nanometric particulates
was based on the powder metallurgy route.
The benefits of nanometric reinforcement can be seen from secondary phases
formed during heat treatment of precipitation-hardened aluminium alloys. The fine
particles formed during heat treatment of such alloys are able to impede dislocation
motion and produce significant improvement in mechanical properties. However, most
precipitates are not chemically stable at elevated temperature, leading to their
dissolution or coarsening [2], and subsequently a decrease in strength.
The introduction of chemically stable, insoluble reinforcement has the potential
to overcome this problem. In experiments with sintered aluminium powder materials,
fine alumina reinforcement formed from the densification of oxidized aluminium
2
Introduction
powder has shown to be capable of pinning grain boundaries during recrystallization,
resulting in stable fine grains and additional grain boundary strengthening.
Accordingly, the primary aim of the present study was to synthesize aluminium
based materials reinforced with different sizes of alumina particulates using an
innovative disintegrated melt deposition technique followed by hot extrusion.
Phase I & II of the present project involves varying the extrusion temperature
and ratio of aluminium respectively. The purpose was to obtain as fine matrix
microstructure as possible. The samples obtained from both phases were characterized
for their microstructural, physical and mechanical properties with respect to the effect
of different extrusion temperatures and ratios used. The optimal and feasible extrusion
parameters were used to process the composites containing different length scales of
reinforcement.
Alumina is not wetted by aluminium in normal foundry temperatures. The
problem of wettability of ceramic particulates is even more severe for the nanosized
particulates used in the present study. Phase III investigates the effect of the addition of
magnesium as a wetting reagent on the incorporation of alumina in an aluminium melt.
The samples obtained were characterized for their microstructural, physical and
mechanical properties with respect to the effect of different magnesium contents in the
aluminium matrix. The optimal magnesium weight fraction was determined and used
to process the composites in Phase IV.
Phase IV investigates the effect of the size of alumina reinforcement on the
properties of the composite. The samples obtained were characterized for their
microstructural, physical and mechanical properties with respect to the effect of
different alumina reinforcement size in the aluminium matrix.
3
Chapter 2: Literature Research
Chapter 2
Literature Research
2.1
Processing Methods
Processing of MMCs can be done using a number of techniques which can be
grouped under: (a) solid state, (b) semi-solid state and (c) liquid state categories [3].
The selection of the processing technique is very important since the resultant
microstructural features are highly dependent on it. With such a wide range of
processing routes available, the appropriate choice will depend on the application and
acceptable cost.
2.1.1 Solid State Processing
Solid state processes are generally used to obtain the highest strength properties
in MMCs because segregation effects and brittle reaction product formation are at a
minimum for these processes when compared to liquid state processes. The main solid
state processes are:
•
Powder metallurgy
•
Diffusion bonding
•
Mechanical Alloying
2.1.1.1 Powder Metallurgy
Powder metallurgy is the most commonly used method in solid state processing
[4]. Metal powder is first blended with reinforcement particulates. A cold isostatic
pressing is utilized to obtain a green compact that is then thoroughly outgassed and
forged or extruded. When hot isostatic pressing is required, the powder blend must
first be outgassed. The main advantages of the powder metallurgy process are: (a) it
5
Literature Research
allows any alloy to be used as the matrix, (b) it allows any type of reinforcement to be
used because reaction between matrix and reinforcement can be minimized by working
below the matrix solidus temperature, and (c) high volume fractions of reinforcement
are possible, thus maximizing the improvement of the properties of the matrix. The
main difficulty in this process is the removal of the binder used to hold the powder
particles together. These organic binders often leave residual contamination that causes
deterioration of the mechanical properties of the composite. The other disadvantages
are the: (a) inherent danger when handling large quantities of highly reactive powders,
(b) the complexity of the manufacturing route and (c) the limitation of the initial
products forms it can produce [3]. As a result, the product is expensive in comparison
with liquid state methods.
2.1.1.2 Diffusion Bonding
Diffusion bonding is used for consolidating alternate layers of foils and fibers
to create single or multiple-ply composites. This is a solid state creep deformation
process. After creep flow of the matrix occurs between the fibers to make complete
metal-to-metal contact, diffusion occurs across the foil interfaces. This process
combines the advantages of ease of processing a wide variety of matrix metals, and the
control of orientation and volume fraction of the fibers. The main problems associated
with this process are fiber degradation and thermal expansion mismatch. Fiber-matrix
interfacial reactions during diffusion bonding can cause degradation of the fiber
interface region and reduce its load carrying ability. Thermal expansion mismatch
between fiber and matrix can often cause tensile stresses and matrix cracking when
cooling from the diffusion bonding temperature.
6
Literature Research
2.1.1.3 Mechanical Alloying
In this method, a high-energy impact mill is used to continuously fragment and
reweld powder particles as fresh internal surfaces are exposed. Frictional heating at the
particle interface causes local melting and consolidation, and rapid heat extraction by
the cooler particle interior causes rapid solidification. Hence, composites produced by
this method are often strong due to high dislocation density and homogenous due to
the thorough mixing of the constituents. The main disadvantage of this process is the
reduced ductility of its products.
2.1.2 Semi-solid Processing
Semi-solid processes were investigated in the early 1970s [5]. One such
process is known as compocasting. It differs from conventional casting in that semisolid alloys are used. In this method, liquid alloy at a temperature slightly above the
liquidus is vigorously agitated and allowed to slowly cool to the semi-solid range. The
alloy exhibits thixotropic behavior, that is, its viscosity decreases when agitated. The
continued agitation prevents a rise in viscosity and breaks up the solidifying dendrites
into fine, spheroidal particles. Reinforcement particles are added to the slurry during
the stirring stage. The viscosity of the slurry inhibits ceramic particle settling and
floating, and can be used to retain particles in the melt. Compocasting has been shown
to be an effective processing scheme with acceptable economics but it faces the
quality-related problems of uneven distribution of particles and high levels of porosity
[6].
7
Literature Research
2.1.3 Liquid State Processing
Liquid state processes can be classified by the method used to physically
combine the matrix and reinforcement. They can be divided into four major categories:
(a) dispersion, (b) infiltration, (c) spraying and (d) in-situ fabrication.
2.1.3.1 Dispersion Process
In dispersion processes, the metallic matrix is superheated in the molten range
and the reinforcement is subsequently incorporated in loose form. Most metalreinforcement systems exhibit poor wetting so mechanical agitation is required to
combine the 2 phases. Surface modification of reinforcement particulates or the
addition of wetting agents to the melt can also help the incorporation and retention of
reinforcement in the matrix. There are several techniques used to incorporate the
reinforcement particulates into the matrix melt [7]. These often proprietary methods
include:
•
Injection of particulates entrained in an inert carrier gas into the melt
with the help of an injection gun. The particulates mix into the melt as
the bubbles ascend through the melt.
•
Addition of particulates into the molten stream as it fills the mold.
•
Addition of particulates into the melt via a vortex introduced by
mechanical agitation.
•
Addition of small briquettes, co-pressed aggregates of matrix alloy
powder and reinforcement particulates, into the melts while stirring.
•
Dispersion of the fine particulates in the melt using centrifugal
acceleration.
8
Literature Research
•
Pushing the particulates into the melt using reciprocating rods.
•
Injection of the particulates into the melt while the melt is continuously
irradiated with high intensity ultrasound.
•
Zero-gravity processing, which involves utilizing a synergism of ultrahigh vacuum and elevated temperature for prolonged periods of time.
Dispersion processes are the most inexpensive way to produce large quantities
of MMCs. The main disadvantages include: (a) the settling of reinforcement
particulates and (b) the limited volume fraction of reinforcement that can be
incorporated. Settling of reinforcement occurs as a result of density difference between
reinforcement particulates and the matrix melt. The volume fraction of reinforcement
is limited because the viscosity of the melt increases with particle incorporation and
becomes non-Newtonian [3]. As a result, the power requirements necessary for mixing
limits the amount of reinforcement that can be incorporated.
2.1.3.2 Infiltration
Infiltration processes involve holding a porous body of the reinforcing phase
within a mold and infiltrating it with molten metal that flows through the interstices to
fill the pores and produce a composite. Depending on the external forces applied to the
metal, the infiltration process can have several variations. In pressureless infiltration,
the metal is allowed to spontaneously infiltrate the reinforcement. However, pressure is
usually applied for benefits such as increased processing speed, control over chemical
reactions, refined matrix microstructures and better soundness of the product. For some
matrix-reinforcement systems, creating a vacuum around the reinforcement provides
the necessary pressure difference to drive infiltration. Pressure can also be applied by a
9
Literature Research
gas, mechanical means, vibrations, centrifugal forces and electromagnetic body forces.
The advantages of infiltration processes include: (a) near-net shape production of parts
and (b) its ability to selectively reinforce metallic matrix with a variety of materials. If
cold dies and reinforcements are used, or if high pressures are maintained during
solidification, matrix-reinforcement chemical reactions can be minimized and defectfree matrix microstructures can be achieved. A limitation is the need for the
reinforcement to be self-supporting. The application of pressure also has the tendency
to induce preform breakage during infiltration, resulting in heterogeneity.
2.1.3.3 Spraying
In spraying processes, droplets of molten metal are sprayed together with the
reinforcing phase and collected on a substrate where metal solidification is completed
[8]. Alternatively, the reinforcement may be placed on the substrate and molten metal
is sprayed onto it. The main advantage of spray processes is the high solidification rate
of droplets produces materials with little segregation and a refined grain structure [9].
Contact time between the melt and the reinforcing particles is also brief, so reaction
between the two is limited and a wider range of reinforcements are possible. The major
disadvantages include limitation of product to simple shapes and the presence of
residual porosity. The process is also not economical due to the high cost of gases used
and the large amounts of waste powder to be collected and disposed.
2.1.3.4 In-situ Fabrication
In-situ processes involve the synthesis of composites such that the
reinforcement is formed in the melt during the processing. An example of an in-situ
10
Literature Research
process is the XD process. The XD process is a patented composite manufacturing
method in which ceramic particles, such as TiB2 and TiC, are produced in situ in a
melt. The process consists of adding compounds to a solvent metal to generate an
exothermic reaction and produce the required reinforcing particles. Alternative
methods are Self-propagation High temperature Synthesis (SHS) and gas injection
[10]. A major advantage of in-situ composite materials is that the reinforcing phase is
homogenously distributed, and the spacing or size of the reinforcement may be
adjusted by the solidification or reaction time. The particles produced are inherently
wetted by the matrix and therefore possess high interfacial strength [11]. The main
disadvantages of this method are the high viscosity of melts, limitation in choice of
reinforcement-matrix systems, and difficulty in controlling the kinetics of the process.
2.1.4 New Innovative Method
In recent years, spraying processes have begun to attract attention among
researchers. The benefits of microstructural refinement, reduced segregation and
minimal interfacial reactions give it great potential as a fabrication technique for
MMCs. A new variant of spray processing was developed recently, which brings
together the cost-effectiveness of conventional foundry processes and the advantages
of spraying processes. This method is known as the Disintegrated Melt Deposition
(DMD) technique [12]. It involves incorporating the ceramic particulates by vortex
mixing. The resulting slurry is then disintegrated by jets of inert gas and subsequently
deposited on a metallic substrate. Unlike conventional spray processes, the DMD
technique employs higher superheat temperatures and lower impinging gas jet velocity.
This process produces only bulk composite material and avoids the formation of overspray powders. It offers both the features of finer grain size and low segregation of
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reinforcement of spray processes, and the simplicity and cost effectiveness of
conventional foundry processes. This technique was thus chosen as the primary
process in the present study to fabricate the composites.
2.2
Types of Reinforcement
The main role of reinforcement in composites used in most engineering
applications is to carry load. Appropriately reinforced materials tend to have higher
strength, stiffness and temperature resistance capabilities when compared to their
monolithic counterparts. The reinforcements for MMCs can be broadly divided into
five categories:
•
Continuous fibers
•
Metal wires
•
Whiskers
•
Short fibers
•
Particulates
2.2.1 Continuous fiber
Continuous fiber reinforcements frequently used in composites include boron
in tungsten and silicon carbide fibers in tungsten [13]. The basic requirements for fiber
reinforcement are high strength, high elastic modulus and low density. In addition, the
melting temperature of the fibers has to be higher than that of the matrix, and the fibers
are expected to be compatible with the matrix from the points of view of technology
and lifetime. Continuous fiber MMCs exhibit very good directional properties.
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However, the high cost of continuous fiber reinforcement and labor-intensive
fabrication routes put them at disadvantage for most commercial applications [14].
2.2.2 Metal wires
Metal wires that have been investigated by researchers include tungsten and
steel [15]. The good ductility of metal wires makes them an ideal reinforcement for
composites carrying tensile load. However, their high density and significant metal-tometal reaction at elevated temperatures lead to fabrication problems, thus limiting their
use.
2.2.3 Whiskers
Whiskers are characterized by their fibrous, single-crystal structures which
have almost no crystalline defects. They are needle-like crystals, having an aspect ratio
ranging from 100 to 15000 [16]. Due to their small size, whiskers are either free of
dislocations or the dislocations they contain do not significantly affect their strength,
which approaches the theoretical strength of the material. Numerous materials,
including metals, oxides, carbides, halides and organic compounds have been prepared
under controlled conditions in the form of whiskers. Silicon carbide whiskers are most
commonly used as reinforcement in composites.
2.2.4 Short fibers
Short fibers are longer than whiskers. Their length is longer than the critical
length Lc (Lc = dσf/σm where d is the fiber diameter, σf is the reinforcement strength
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and σm is the matrix strength) and their aspect ratio ranges from 20 to 60. In a given
fiber, if the mechanical properties improve as a result of increasing the fiber length,
then it is denoted a short fiber. The oxide fibers, Saffil and Kaowool, are used mainly
for the reinforcement of automobile engine components. While short fibers are cheaper
than both whiskers and continuous fibers, they are also less effective as reinforcement.
2.2.5 Particulates
Particulate reinforced metals, with their advantages of low cost, high modulus
and strength, high wear resistance, are more viable for commercial use. The lower
fabrication costs come about due to the low cost and easy availability of reinforcement,
and the ability to utilize existing conventional metallurgical processes such as forging,
rolling, extrusion, etc. Particulate reinforced materials are also attractive because they
exhibit more isotropic properties [17] as a result of their random distribution and low
aspect ratio of the particulates. Particulates such as oxides, carbides, nitrides, borides
and elemental materials have been extensively investigated as reinforcement by
researchers worldwide.
With all the advantages of using particulate reinforcement, it can be expected
that much of the current research and commercialization will lean toward this area of
study. From the above description, the possibilities of particulate reinforced MMCs
might seem boundless. In reality, the choice of reinforcement is dictated by several
factors [3]:
1. The application – If the composite is to be used in a structural
application, a low density and high modulus reinforcement should be
used.
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2. Particle size and shape – Angular particles can act as local stress raisers,
reducing the ductility of the composite. For composites processed in the
molten state, coarser particles are generally easier to be incorporated but
are more susceptible to gravity settling, leading to segregation in the
casting. Finer particles increase the viscosity of the melt, making
processing difficult.
3. Coefficient of thermal expansion (CTE) – If the composite is to be used
in thermal applications, the CTE and thermal conductivity are
important. The CTE also influences the strength of the composite.
4. Compatibility with matrix material – Reaction of the reinforcement
with the matrix can severely degrade the properties of the resultant
composite.
5. Cost – A major reason for using particles as reinforcement is to reduce
the cost of the composite. To keep in line with that objective, the
reinforcement has to be readily and cheaply available.
From the considerations above, Al2O3 and SiC particulates have emerged as the
most widely used reinforcements in aluminium-based MMCs. Due to the wide range
of grades available, Al2O3 particulates were selected as the reinforcement phase in the
present study.
2.3
Thermomechanical Processes
One of the advantages of particulate MMCs is that raw ingots obtained from
primary processing can be processed into usable shapes and sizes by employing
conventional metal forming technologies. Control of parameters of these
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thermomechanical processes will determine the resultant microstructures of the
composite.
Metal forming processes can be classified into hot-working and cold-working
operations depending on the temperature conditions [18]. Hot-working refers to
deformation carried out under conditions of temperature and strain rate such that
recovery processes occur substantially during the deformation process so that large
strains can be achieved with essentially no strain hardening. Cold-working is
deformation carried out under conditions where recovery processes are not effective.
In hot-working, the strain hardening and distorted grain structure produced by
deformation are very rapidly eliminated by the formation of new strain-free grains as a
result of recrystallization. Very large deformations are possible in hot-working because
the recovery processes keep pace with the deformation. Hot-working occurs at an
essentially constant flow stress and the energy required for deformation is generally
less than that for cold-working. Since strain hardening is not relieved in cold-working,
the flow stress increases with deformation. Hence, total deformation without causing
fracture is less for cold-working.
The extrusion method is used in the present study as the secondary process.
Extrusion is a common metal shaping process used for wrought MMCs. The reaction
of the extrusion billet with the container and die results in high compressive stresses
which are effective in reducing the cracking of materials during primary breakdown
from the ingot. Extrusion can also reduce particle clustering and create a more uniform
reinforcement distribution. There is a complex interrelationship between extrusion
ratio, working temperature, speed of deformation, and frictional conditions at the die
and container wall. The selection of optimum process variables for billet size in the
present study has to be determined by trial and error.
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2.4
Interface Characteristics
The interface formed between the matrix and reinforcement is of great
importance since the characteristics of this region affect the load transfer and crack
resistance of the composite during deformation [19]. In order to maximize interfacial
bonding in composites, it is necessary to promote wetting, control chemical
interactions and minimize oxide formation.
Wetting of ceramics by molten metals is often defined in terms of a contact
angle less than 90° for a liquid metal droplet on a ceramic substrate as determined by
the sessile droplet test [20]. For unreactive metals and those that do not form an oxide
film, this method of quantifying wettability is satisfactory. For reactive metals, in
particular Al, Mg and Ti, problems with the exclusion of oxygen from the system
means that most ceramic reinforcements are considered to be non-wettable at
reasonable processing temperatures [21]. Under normal casting conditions, few
ceramic particles can be spontaneously incorporated into liquid metals without the use
of externally applied forces. By careful use of fluxes, gas shields and vacuum melting
procedures, oxide barriers may be minimized but any inherent, non-wettability of the
ceramic makes particle entry into the melt difficult. To fully overcome both
mechanical and thermodynamic obstacles to particle entry, energy is usually supplied,
most commonly in the form of vigorous stirring or pressure during infiltration, in
conjunction with melting in a controlled atmosphere.
It is commonly observed that non-wetting particles, or particles that have been
incorporated with an oxide film enveloping their surface, often cluster or are rejected
from the liquid once the externally applied force is removed. Therefore, it is clear that
spontaneous incorporation of the particles into the melt is desirable if uniform particle
distributions are to be achieved.
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Wetting can be improved in a system by promoting a decrease in the contact
angle through the various methods:
•
Increasing the surface energy of the solid.
•
Decreasing the solid-liquid interfacial energy.
•
Decreasing the surface tension of the liquid.
In the case of ceramic reinforcement in molten metal, the following techniques
can be utilized to improve wetting [7]:
•
Metallic coating on the ceramic particles.
•
Alloying of the metallic matrix with reactive materials.
•
Heat treating the ceramic particles.
•
Ultrasonic vibration of the melt.
Chemical coating, chemical vapor deposition, physical vapor deposition and
plasma spraying are the common methods of coating reinforcement particulates. The
application of metallic coatings, such as nickel and copper, to the ceramic particulates
increases the overall surface energy of the particulates by altering the nature of the
interface from metal-ceramic to metal-metal.
The addition of reactive elements such as Mg, Ca, Ti, Zr and P improves
wettability by reducing the surface tension of the melt, decreasing the solid-liquid
interfacial energy or inducing wettability by a chemical reaction. Very small quantities
of reactive elements are sufficient to improve wetting since they segregate either to the
melt surfaces or at the melt-ceramic interface. While the formation of interfacial
reaction products is necessary for obtaining a strong interface, the amount of reaction
at the interface must be controlled. During the production of MMCs, control of the
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reaction layer thickness and morphology may be difficult. Excessive formation of
reaction products may be detrimental to the mechanical properties of the composite.
Heat treatment of particulates before their dispersion in the melt aids their
incorporation by causing desorption of adsorbed gases from the ceramic surfaces.
Ultrasonic vibrations promote wetting by a similar mechanism to heat treatment. In
addition, they also supply energy for melt cavitation which facilitates particulate
dispersion in the melt.
From the above considerations, it was decided to investigate the effect of
magnesium addition on the incorporation of difficult to wet nanosize alumina in an
aluminium matrix. Alumina particulates were also preheated to improve wettability in
the Al-Mg melt in accordance with the fundamental principles discussed above.
2.5
Effect of Reinforcement Size
The main strengthening mechanisms in discontinuously reinforced MMCs
containing particulates 1-100µm in size are load transfer from the matrix to the
reinforcement, constrained matrix flow and dislocation strengthening by loops
punched due to the difference between the thermal expansion of the two phases [22].
Orowan strengthening is negligible in MMCs due to the large interparticle distance
resulting from the large reinforcement size [23]. Only recently have researchers
explored particulate reinforcements smaller than 1µm for MMCs. Geiger and Walker
[24] found that the strength and ductility at room temperature of aluminium with 20
vol. % SiCp increased as the particulate size decreased. This trend occurred until the
finest size of 0.7µm SiC was used. Tan et al. [25] reported a modest increase in proof
stress with 20 vol. % 0.08µm SiCp added to aluminium. Arsenault investigated
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Literature Research
aluminium containing 20 vol. % 0.5µm SiCp and found a large increase in proof stress
[26]. Ductility of matrices decreased but remained in useful range when reinforced
with submicron particulates. An aluminium reinforced with 1 vol. % 25-30nm Si-N-C
composite was found to exhibit tensile strength comparable to composites reinforced
with much higher volume fractions of coarser particulates [27]. Interestingly, the finer
particulates were able to produce the same strength increase with a less severe decrease
in ductility. During plastic deformation of MMCs, large particles will cavitate before
smaller ones. Hence, matrices reinforced with smaller particles are theoretically able to
accommodate more strain before cavitation occurs. In practice, tendency of particle
clustering increases when particle size decreases. The loss of homogeneity is
detrimental to mechanical properties and depending on severity, is able to offset the
improvement in ductility brought about by the reduction in particle size. In the above
studies, the composites were fabricated by powder metallurgy and they indicate that
the strengths of particulate composites tend to increase with decreasing particle size.
2.6
Summary
From the literature research carried out, it was found that no efforts have been
made to assess the feasibility of fabricating MMCs with nanometric reinforcements
using liquid state processing. Accordingly, the main focus of research was to
investigate the effect of nanometric reinforcements and their length scale on physical
and mechanical properties of an aluminium alloy. Present research show promising
results achievable only with the powder metallurgy processing route. This study holds
great potential to develop an economical, reinforced material for specific strengthcritical applications targeted for the aerospace, automobile, sports, machinery and
energy sectors. The present study was thus focused on the feasibility of producing
Al/Al2O3 nanocomposites by the DMD technique.
20
Chapter 3: Materials and Experimental Procedures
Chapter 3
Materials and Experimental Procedures
Materials used in this experiment were obtained from the Materials Science
Laboratory in NUS. The Disintegrated Melt Deposition (DMD) technique was
employed for the synthesis of the materials. For Phases I and II, aluminium was
deposited, followed by extrusion at different temperatures and extrusion ratios
respectively. For Phases III and IV, Al-Mg/Al2O3 composites and monolithic Al-Mg
were synthesized, followed by extrusion at a selected temperature and extrusion ratio
determined in Phases I and II. All fabrication was done within NUS. An overview of
the experiments carried out is shown in Figure 3-1.
3.1
Materials
This study comprised of the following 4 phases:
(a) Phase I – Investigate the effect of extrusion temperature on the microstructure and
properties of pure Al.
(b) Phase II – Investigate the effect of extrusion ratio on the microstructure and
properties of pure Al.
(c) Phase III – Investigate the effect of magnesium addition on the incorporation of
Al2O3 and properties of Al/Al2O3 composite.
(d) Phase IV – Investigate the effect of reinforcement size on the resultant properties of
Al/Al2O3 composite.
A summary of the materials fabricated is shown in Table 3-1. All casting log
sheets recording the synthesis parameters are shown in Appendix A. Note that the
experiment was designed such that sample Al-3.4Mg/Al2O3 (0.05µm Al2O3) in Phase
III, when included with the other samples in Phase IV (0.3µm, 1µm and 10µm), will
22
Materials and Experimental Procedures
form a complete set of experiments in which the reinforcement particulate size is
varied from 0.05µm-10µm. Aluminium obtained from CERAC Incorporated, USA
(99.9% pure) was used in Phases I and II and came in the form of 2-10mm granules
(See Figure 3-2). The Al2O3 particulate reinforced aluminium-magnesium composite
material fabricated in Phases III and IV used the same aluminium. Magnesium
turnings (99.9% pure) obtained from Acros Organics, New Jersey, USA, were used to
improve the wettability of alumina in the aluminium matrix. The alumina
reinforcement obtained from Baikowski, Japan came in particle sizes of 0.05µm,
0.3µm, 1µm and 10µm.
23
Materials and Experimental Procedures
Phase I & II
Synthesis of Aluminium
Phase I
Extrusion at different
temperatures
Phase II
Extrusion at different
ratios
Specimen Preparation
Specimen Preparation
Characterization of Specimens
Characterization of Specimens
•Density & Porosity Measurements
•Microstructure Characterization
•Thermal Mechanical Analysis
•Hardness Measurements
•Tensile Testing
•Fractography
•XRD
•Density & Porosity Measurements
•Microstructure Characterization
•Thermal Mechanical Analysis
•Hardness Measurements
•Tensile Testing
•Fractography
•XRD
Analysis of Results
(Determine optimum extrusion parameters)
Phase III & IV
Synthesis of Composite
Phase III
Different Quantity of
Magnesium
Phase IV
Different Size of Al2O3
Specimen Preparation
Specimen Preparation
Characterization of Specimens
Characterization of Specimens
•Density & Porosity Measurements
•Microstructure Characterization
•Thermal Mechanical Analysis
•Hardness Measurements
•Quantitative Assessment:
•Reinforcement
•Wetting Agent
•Tensile Testing
•Fractography
•XRD
•Density & Porosity Measurements
•Microstructure Characterization
•Thermal Mechanical Analysis
•Hardness Measurements
•Quantitative Assessment:
•Reinforcement
•Wetting Agent
•Tensile Testing
•Fractography
•XRD
Analysis of Results
Figure 3-1
Flow chart showing the overview of the project.
24
Materials and Experimental Procedures
Table 3-1
Phase
Summary of materials fabricated in study.
Metallic Matrix
Reinforcement
I
Al
-
II
Al
-
Al-1.6Mg
Al-2.9Mg
Al-3.4Mg
Al-3.79Mg
Al-3.87Mg
Al-3.91Mg
Al-4.07Mg
0.05µm Al2O3
0.05µm Al2O3
0.05µm Al2O3
0.3µm Al2O3
1µm Al2O3
10µm Al2O3
III
IV
Figure 3-2
Designation
Al25
Al85
Al150
Al250
Al350
Al-7
Al-8 (Al85)
Al-10
Al-1.6Mg/Al2O3
Al-2.9Mg/Al2O3
Al-3.4Mg/Al2O3
Al-Mg
Al-Mg-0.3µm Al2O3
Al-Mg-1µm Al2O3
Al-Mg-10µm Al2O3
Raw materials used: Aluminium granules, magnesium turnings and
alumina.
25
Materials and Experimental Procedures
3.2
Synthesis
The DMD technique was used to synthesize the materials in this study. Figure
3-3 shows a schematic diagram of this technique.
Motor
Vibratory Feeder
Thermocouple
Crucible Lid
Argon
Gas
Tank
Stirrer
Resistance Furnace
Graphite Crucible
Pouring Nozzle
750 oC
Molten
Slurry
Ar
Ar
Argon-filled
Chamber
Deposited Ingot
Substrate
Figure 3-3
Schematic diagram of the experimental set-up for the DMD casting.
For the synthesis of Al-Mg/Al2O3 composites, the aluminium granules,
magnesium turnings and Al2O3 particulates were weighed before processing. The
Al2O3 particulates were preheated for an hour at 500°C to remove moisture and
improve wettability. A crucible was placed in a large electric resistance furnace as
shown in Figure 3-4. A thermocouple and stirrer were placed into position in the
26
Materials and Experimental Procedures
crucible, followed by the aluminium granules and magnesium turnings. Finally, a mild
steel cover was placed above the crucible and a ceramic tube that pumps in argon gas
was inserted to create an inert environment. This was done to minimize the oxidation
of raw materials during synthesis.
Figure 3-4
Resistance furnace used for DMD.
The synthesis procedure involved heating the aluminium granules and
magnesium turnings to 750°C under an inert atmosphere in a graphite crucible. The
Al2O3 particulates were then added to the molten aluminium via a vibratory feeder.
While the particulates were incorporated, the melt was continuously stirred at 450rpm
using a twin blade (pitch 45°) mild steel stirrer. The melt was stirred to facilitate the
incorporation and uniform distribution of the Al2O3 particulates in the metallic matrix.
The stirrer was coated with Zirtex 25 (86% ZrO2, 8.8% Y2O3, 3.6% SiO2, 1.2% K2O
and Na2O, and 0.3% trace organic) to avoid possible iron contamination of the molten
aluminium. The total time for the addition of Al2O3 particulates was limited to a
maximum of 10 minutes to avoid the formation of significant interfacial reaction
27
Materials and Experimental Procedures
products. Following stirring, the composite melt was poured through a 10mm centrally
drilled hole in the base of the graphite crucible. The resultant melt stream was
disintegrated using 2 linear argon gas jets orientated normal to the melt stream and
located at a distance of 0.265m from the melt pouring point. The argon gas was
delivered to the melt disintegration point at a flow rate of 25lmin-1 by a pair of 4mm
diameter nozzles. The disintegrated melt slurry was subsequently deposited on a
circular shaped metallic substrate located 0.5m from the disintegration point. The
components of the mold and metallic substrate are shown in Figure 3-5.
The synthesis of Al and Al-Mg ingots were carried out using the same method
as described above but without the addition of Al2O3 particulates.
All solidified performs obtained in this study were in the form of ingots with a
diameter of 40mm and lengths varying from 200-450mm. The various tools used for
the fabrication of the material can be seen in Figure 3-6.
Figure 3-5
Components of mold and metallic substrate.
28
Materials and Experimental Procedures
Figure 3-6
3.3
Tools used in fabrication (from back): Graphite crucible fitted with
nozzle/plug and mild steel lid, ceramic tube, mild steel stirrer,
thermocouple.
Specimen Preparation
Shrinkage cavities located at the top of the ingots were removed using a FORM
2-LC Charmilles Technologies electrical discharge wire-cutting machine (EDM). They
were then were turned down to a diameter of 35mm using a lathe machine and cut up
into shorter sections using EDM. EDM wire-cutting was used because of the relatively
smooth work surface produced and minimal gap of cut, which translate to reduced
material wastage.
3.4
Extrusion
Cylindrical samples of approximately 35mm in diameter and 40mm in height
were cut by EDM. For Phase I, these were extruded at 350°C, 250°C, 150°C, 85°C and
25°C on a 150 ton hydraulic press using colloidal graphite as lubricant. The samples
were extruded into 8mm diameter rods by employing an extrusion ratio of 20.25:1.
29
Materials and Experimental Procedures
Samples in Phase II were extruded as in Phase I but at extrusion ratios of 12.96:1,
20.25:1 and 26.45:1 at a temperature of 85°C. In Phases III and IV, extrusion was
carried out at 250°C with an extrusion ratio of 20.25:1. Prior to their extrusion, each of
the specimens was coated with graphite lubricant and preheated to their respective
extrusion temperatures in a resistance furnace for 1 hour. The extruded rods were then
cut up into smaller sections for the subsequent characterization tests.
3.5
Quantitative Assessment of Reinforcement
Image analysis using Scion image analysis system was used to determine the
size and volume fraction of alumina particulates in the aluminium matrix of reinforced
samples. The procedure involved digitizing the scanning electron micrographs into
binary images followed by cumulative analysis of all the images. A total of fifteen
representative scanning electron micrographs for each of the composites were used for
the purpose of image analysis.
3.6
Quantitative Assessment of Alloying Element
The magnesium retained in the samples of Phases III & IV was determined by
the inductively coupled plasma atomic emission method using inductively coupled
plasma spectrometer (Thermo Jarrell Ash, IRIS AP Duo OES). This method involved:
(a) dissolving a known amount of sample in nitric acid, (b) atomizing the solution into
plasma, and (c) analyzing the plasma in an inductively coupled plasma spectrometer
which detects the wavelength of magnesium.
30
Materials and Experimental Procedures
3.7
Density Measurement
Density measurements were carried out on polished samples of monolithic and
composite materials taken from extruded rods. This was carried out in accordance to
the Archimedes’ principle [28]. Distilled water was used as the immersion fluid. An
A&D Model ER-182A electronic balance with ±0.0001g accuracy was used for all
weight measurements. The setup for the measurement can be found in Appendix B.
3.8
Microstructure Characterization
Scanning electron microscopy was performed on samples to investigate
reinforcement distribution, grain size and morphology of the matrix, and presence of
porosity. The JEOL JSM-5600 LV Scanning Electron Microscope (SEM) equipped
with Energy Dispersive Spectroscopy (EDS) was used. The extruded samples were
metallographically polished prior to examination. They were then etched using
Keller’s reagent (0.5 vol. % HF, 1.5 vol. % HCl, 2.5 vol. % HNO3 and 95.5 vol. %
H2O). The Hitachi S4100 Field-Emission Scanning Electron Microscope (FESEM)
was used to investigate the nanometer-sized reinforcement in Phase III.
Image analysis using the Scion image analysis system was used to determine
the grain size and volume fraction of porosity in the extruded samples. A total of 15
representative scanning electron micrographs for each sample were used for image
analysis.
3.9
X-ray Diffraction Studies
X-Ray diffraction studies were carried out using an automated Shimadzu Lab-
X XRD 6000 diffractometer. Samples of 5mm thickness were exposed to CuKα
31
Materials and Experimental Procedures
radiation (λ = 1.5418Å) using a scanning speed of 2°min-1. A plot of intensity versus
2θ (2θ represents the Bragg angle) was obtained, illustrating peaks at different Bragg
angles (see Appendix C). The Bragg angles and the values of interplanar spacing (d)
obtained from the plot were matched with standard values for aluminium and other
expected phases [29].
3.10 Mechanical Testing
3.10.1
Microhardness Measurement
The microhardness measurements (see Appendix D) were conducted on a
digital microhardness tester (Model MXT50) developed by Matsuzawa of Japan. The
tester makes use of a pyramidal diamond indenter with a facing angle of 136°.
Microhardness measurement was carried out using a test load of 25gf and a dwell time
of 15s on the matrix. The test samples were polished with 5 micron alumina
suspension prior to measurement.
3.10.2
Macrohardness Measurement
The macrohardness of the samples was measured using the Future-Tech Model
FR-3 Rockwell Type Hardness Tester. Macrohardness measurement (see Appendix E)
was carried out using the Rockwell 15T superficial scale which uses a 1.58mm
diameter steel ball indenter with a 15kgf test load, following the ASTM Standard E1894. The test samples were polished with 5 micron alumina suspension prior to
measurement.
32
Materials and Experimental Procedures
3.10.3
Tensile Testing
Tension tests were performed to obtain information of the strength and ductility
of the material under uniaxial tensile stress. The round tensile test specimens were
obtained from the extruded rods. They were machined to a diameter of 5mm and gauge
length of 25mm using CNC machines based on the dimensions given in Appendix F.
The tensile tests were carried out on an automated servo-hydraulic Instron 8501 testing
machine in accordance to the ASTM test method E8M-96 for tension testing of
metallic materials. An Instron 2630-100 Series Clip-on type extensometer was used to
maintain a crosshead speed of 1.69 x 10-4s-1. The stress versus strain curves were then
plotted and utilizing the offset method, the 0.2% yield strength of the samples was
obtained. The ultimate tensile strength (UTS) and failure strain (FS) were also read
from the graphs (see Appendix G).
3.10.4
Dynamic Elastic Modulus Testing
Dynamic elastic modulus measurements were made on the extruded rods of
each specimen using the Free-Free beam method in accordance with the ASTM
C1259-96 standard. The steps involved are as follows:
1. The rods were suspended at the nodal points (0.22L and 0.78L where L is the
length of the rod) using nylon threads.
2. Excitation was provided using a modally tuned hammer equipped with a load
sensor at the tip.
3. The first mode of flexural vibration was captured by accelerometer located at
the end of the rod.
33
Materials and Experimental Procedures
The frequency response function (Bode plot) obtained was used to determine
the natural frequency (ωn). The natural frequency obtained was then used to determine
the dynamic elastic modulus using the following equation:
2
ω n
4
2
ρL
(
)
L
β
n
E=
I
where L represents the length of the beam, I is the inertia of the cross section of the
beam, ρ is the density of the material and βn is a constant.
3.11 Fractography
Fracture surface characterizations were conducted on the fractured tensile
specimens to provide an insight into the various possible fracture mechanisms
operative during the tensile loading. The fracture surfaces were viewed in the JEOL
JSM-5600 LV SEM.
3.12 Thermal Mechanical Analysis
The thermal mechanical analysis study was carried out using the Setaram 92
TMA 16-18 thermomechanical analyzer that uses a hemispherical ended, 5mm
diameter, alumina probe. The top and bottom surfaces of the test specimens were
ground with a 300 grit SiC abrasive paper to ensure that the specimen surfaces were
flat. A sample height of 8mm was used in all the tests. A test sequence of temperature
range 50°C to 400°C was used for each of the extruded specimens. The temperature
was measured by a K-type, coaxial thermocouple and the test was carried out in an
inert environment of argon gas. The heating rate of the samples was maintained at
34
Materials and Experimental Procedures
5°Cmin-1 while the argon gas flow rate was maintained at 1.2lmin-1. The data was
obtained in the form of curves of dimensional change versus temperature and time.
The Setaram software was used to calculate the average coefficient of thermal
expansion (CTE) of the samples (see Appendix H).
35
Chapter 4: Results
Chapter 4
Results
4.1
Phase I & II Results
4.1.1 Processing
Macrostructural characterization conducted on the as-cast samples did not
reveal any presence of macropores. Solidification shrinkage cavity was present in all
the as-cast ingots. Following extrusion, there was no evidence of any macrostructural
defects.
The results from the Phase I extrusion process conducted at different extrusion
temperatures revealed an increase in extrusion load with a decrease in the extrusion
temperature from 350°C to 85°C (See Table 4-1). Results from the Phase II extrusion
process conducted at different extrusion ratios revealed an increase in extrusion load
with an increase in extrusion ratio (See Table 4-2).
4.1.2 Density Measurement
The results of density measurements and porosity calculations for Phase I and
Phase II are shown in Table 4-1 and Table 4-2 respectively. The volume fraction of
porosity was computed from the experimentally determined density values. The results
indicate that near dense aluminium materials can be obtained using the fabrication
methodology adopted in the present study.
37
Results
Table 4-1
Phase I results of density and porosity measurements, and extrusion load
realized. Extrusion ratio of 20.25:1 was used in Phase I.
Al25
Theoretical
Density
(gcm-3)
2.700
Experimental
Density
(gcm-3)
2.696 ± 0.005
Al85
2.700
Al150
Porosity
(vol. %)
Load
(tons)
0.142
70
2.698 ± 0.002
0.083
70
2.700
2.698 ± 0.002
0.072
60
Al250
2.700
2.699 ± 0.001
0.052
50
Al350
2.700
2.695 ± 0.005
0.167
50
Specimen
Table 4-2
Phase II results of density and porosity measurements, and extrusion
load realized. Extrusion temperature was maintained at 85°C.
Al-7
Theoretical
Density
(gcm-3)
2.700
Experimental
Density
(gcm-3)
2.696 ± 0.003
Al-8
2.700
Al-10
2.700
Specimen
Porosity
(vol. %)
Load
(tons)
0.135
80
2.698 ± 0.002
0.083
70
2.697 ± 0.005
0.112
70
4.1.3 Microstructural Characterization
Figure 4-1 shows representative SEM micrographs showing grain morphology
of Al processed in Phase I. Figure 4-2 shows representative SEM micrographs
showing grain morphology of Al processed in Phase II. The grain morphology was
generally equiaxed. The size and aspect ratio of the grains of the extruded samples
from Phase I and Phase II are shown in Table 4-3 and Table 4-4 respectively.
38
Results
Table 4-3
Phase I results of quantitative microstructural characterization.
Al25
Grain Morphology
Size
Aspect Ratio
(µm)
16 ± 3
1.4 ± 0.4
Al85
16 ± 3
1.4 ± 0.4
Al150
20 ± 4
1.7 ± 0.6
Al250
23 ± 4
1.5 ± 0.5
Al350
23 ± 3
1.4 ± 0.4
Specimen
Table 4-4
Phase II results of quantitative microstructural characterization.
Al-7
Grain Morphology
Size
Aspect Ratio
(µm)
12 ± 2
1.4 ± 0.3
Al-8
16 ± 3
1.4 ± 0.4
Al-10
23 ± 5
1.6 ± 0.5
Specimen
39
Results
(a)
(b)
(c)
(d)
(e)
Figure 4-1
Representative SEM micrographs showing grain morphology of Al
extruded with an extrusion ratio of 20.25:1 and temperature of: (a) 25°C,
(b) 85°C, (c) 150°C, (d) 250°C and (e) 350°C.
40
Results
(a)
(b)
Figure 4-2
Representative SEM micrographs showing grain morphology of Al
extruded at 85°C with an extrusion ratio of: (a) 26.45:1 and (b)12.96:1.
41
Results
4.1.4 Mechanical Characterization
4.1.4.1 Hardness
Phase I results of the microhardness and macrohardness measurements (See
Table 4-5) conducted on extruded Al samples revealed a decrease in hardness when
extrusion temperature is increased. Phase II results (See Table 4-6) showed an increase
in hardness when extrusion ratio is increased.
Table 4-5
Phase I results of hardness test.
Al25
Microhardness
(HV)
48.6 ± 2.0
Macrohardness
(HR15T)
58.0 ± 1.0
Al85
46.6 ± 1.5
57.1 ± 1.5
Al150
45.6 ± 1.8
56.1 ± 0.7
Al250
41.3 ± 1.5
51.0 ± 1.3
Al350
36.1 ± 1.2
36.2 ± 1.1
Specimen
Table 4-6
Phase II results of hardness test.
Al-7
Microhardness
(HV)
53.2 ± 1.1
Macrohardness
(HR15T)
58.0 ± 0.4
Al-8 (Al85)
46.6 ± 1.5
57.1 ± 1.5
Al-10
45.5 ± 1.3
55.9 ± 0.5
Specimen
4.1.4.2 Tensile Properties
The results of ambient temperature tensile test for Phase I and Phase II are
shown in Table 4-7 and Table 4-8 respectively. The tensile test curves are found in
Appendix G. Phase I results revealed that a decrease in extrusion temperature led to an
42
Results
increase in the 0.2% YS and UTS of aluminium while the failure strain was adversely
affected. There was no significant change in the elastic modulus.
Phase II results revealed that an increase in extrusion ratio led to an increase in
the 0.2% YS and UTS of aluminium while the failure strain was adversely affected. As
in Phase I, the elastic modulus remained the same.
Table 4-7
Phase I results of ambient temperature tensile test.
Al25
Modulus
(GPa)
71
0.2% YS
(MPa)
166 ± 4
UTS
(MPa)
175 ± 4
Failure Strain
(%)
14.1 ± 0.8
Al85
72
150 ± 11
155 ± 10
15.1 ± 0.1
Al150
73
147 ± 1
158 ± 1
17.0 ± 0.7
Al250
71
132 ± 2
137 ± 2
19.4 ± 0.6
Al350
71
114 ± 5
118 ± 6
25.3 ± 2.8
Specimen
Table 4-8
Phase II results of ambient temperature tensile test.
Al-7
Modulus
(GPa)
72
0.2% YS
(MPa)
167 ± 1
UTS
(MPa)
176 ± 1
Failure Strain
(%)
14.0 ± 0.8
Al-8 (Al85)
72
150 ± 11
155 ± 10
15.1 ± 0.1
Al-10
72
145 ± 1
150 ± 1
15.6 ± 1.4
Specimen
4.1.5 Fractography
The tensile fracture surfaces of samples from Phases I & II are shown in Figure
4-3 to Figure 4-4. These SEM micrographs show deep, equiaxed dimples, indicating a
ductile type of failure mode.
43
Results
(
(a)
(b)
(c)
(d)
(e)
Figure 4-3
Representative SEM micrographs showing the fracture surface of Al
extruded with an extrusion ratio of 20.25:1 and temperature of: (a) 25°C,
(b) 85°C, (c) 150°C, (d) 250°C and (e) 350°C.
44
Results
(a)
(b)
Figure 4-4
Representative SEM micrographs showing the fracture surface of Al
extruded at 85°C with an extrusion ratio of: (a) 26.45:1 and (b) 12.96:1.
45
Results
4.1.6 Thermal Mechanical Analysis
The thermal mechanical analysis revealed that the average coefficient of
thermal expansion (CTE) of the samples did not show any significant change when the
extrusion temperature (See Table 4-9) and ratio (See Table 4-10) are varied. The CTE
values obtained are similar to the CTE of wrought aluminium (25.5 x 10-6K-1 [30]).
This showed that the CTE is not affected by these two extrusion parameters.
Table 4-9
Phase I results of thermal mechanical analysis.
Al25
CTE
(x 10-6K-1)
25.13 ± 1.10
Al85
26.03 ± 0.69
Al150
26.25 ± 1.67
Al250
26.38 ± 0.67
Al350
25.85 ± 0.69
Specimen
Table 4-10
Phase II results of thermal mechanical analysis.
Al-7
CTE
(x 10-6K-1)
25.49 ± 0.88
Al-8 (Al85)
26.03 ± 0.69
Al-10
25.98 ± 0.44
Specimen
46
Results
4.2
Phase III Results
Phase III was aimed to arrive at the matrix composition that allows for the
maximum incorporation of nanosized alumina particulates. Nanosized alumina
particulates (50nm) were chosen as they are most difficult to wet and incorporate. The
amount of added magnesium was restricted to 4 wt. % to minimize the formation of
harder and brittle Al12Mg17 phase.
4.2.1 Processing
Macrostructural characterization conducted on the as-cast samples did not
reveal any presence of macropores. Solidification shrinkage cavity was present in all
the as-cast ingots. Following extrusion, there was no evidence of any macrostructural
defects.
The results from the Phase III extrusion process conducted at an extrusion
temperature of 250°C and ratio of 20.25:1 revealed an increase in extrusion load when
composite magnesium content is increased (See Table 4-12). It may be noted these
extrusion parameters were selected as a further increase in extrusion ratio or a decrease
in extrusion temperature did not allow the successful extrusion of the composite
samples.
4.2.2 Quantitative Assessment of Reinforcement
The results of image analysis on composite samples in Phase III revealed an
increase in amount of alumina incorporation in the matrix when the magnesium
content of the composite is increased. The results are shown in Table 4-11.
47
Results
Table 4-11
Phase III results of quantitative assessment of Mg and Al2O3 in
composites.
Specimen
Al-1.6Mg/Al2O3
Al2O3 content
(vol. %)
(wt. %)
0.67
1.00
Mg content
(wt. %)
1.56
Al-2.9Mg/Al2O3
0.81
1.21
2.94
Al-3.4Mg/Al2O3
0.94
1.40
3.42
4.2.3 Quantitative Assessment of Alloying Element
Results of inductively coupled plasma spectrometer on composite samples in
Phase III showed the successful retention of magnesium in the extruded composite
matrix. The results are shown in Table 4-11.
4.2.4 Density Measurement
The results of density and porosity measurements for Phase III are shown in
Table 4-12. The volume fraction of porosity was measured using image analysis
conducted on 15 representative SEM micrographs. The results indicate that near dense
Al-Mg/Al2O3 materials can be obtained using the fabrication methodology adopted in
the present study. It may be noted that the extrusion load almost reached the limit of
the extrusion machine in the case of Al-3.4Mg/Al2O3 composite.
Table 4-12
Phase III results of density and porosity measurements, and extrusion
load used.
Al-1.6Mg/Al2O3
Experimental
Density
(gcm-3)
2.696 ± 0.011
Al-2.9Mg/Al2O3
2.669 ± 0.009
0.039
120
Al-3.4Mg/Al2O3
2.662 ± 0.009
0.114
130
Specimen
48
Porosity
(vol. %)
Load
(tons)
0.075
100
Results
4.2.5 Microstructural Characterization
Figure 4-5 shows representative SEM micrographs showing grain morphology
of Al-Mg/Al2O3 materials processed in Phase III. The grain morphology was generally
equiaxed. The size and aspect ratio of the grains of the extruded samples from Phase
III are shown in Table 4-13.
Table 4-13
Phase III results of quantitative microstructural characterization.
Al-1.6Mg/Al2O3
Grain Morphology
Size
Aspect Ratio
(µm)
0.5 ± 0.1
1.3 ± 0.2
Al2O3 Particulates Morphology
Size
Aspect Ratio
(µm)
0.053 ± 0.027
1.6 ± 0.3
Al-2.9Mg/Al2O3
0.4 ± 0.1
1.3 ± 0.2
0.051 ± 0.021
1.5 ± 0.4
Al-3.4Mg/Al2O3
0.4 ± 0.1
1.3 ± 0.2
0.050 ± 0.024
1.6 ± 0.5
Specimen
Figure 4-6 shows representative SEM micrographs showing the presence of
uniformly distributed, micron-sized Al12Mg17.
FESEM micrographs (See Figure 4-7) showed uniform distribution of alumina
reinforcement. The size and aspect ratio of the alumina particulates of the extruded
samples are shown in Table 4-13.
49
Results
(a)
(b)
(c)
Figure 4-5
Representative SEM micrographs showing grain morphology of: (a) Al1.6Mg/Al2O3, (b) Al-2.9Mg/Al2O3 and (c) Al-3.4Mg/Al2O3.
50
Results
(a)
(b)
(c)
Figure 4-6
Representative SEM micrographs showing uniform distribution of
intermetallic Al12Mg17 (indicated by arrows) in: (a) Al-1.6Mg/Al2O3, (b)
Al-2.9Mg/Al2O3 and (c) Al-3.4Mg/Al2O3.
51
Results
(a)
(b)
(c)
Figure 4-7
Representative FESEM micrographs showing distribution of alumina in:
(a) Al-1.6Mg/Al2O3, (b) Al-2.9Mg/Al2O3 and (c) Al-3.4Mg/Al2O3.
52
Results
4.2.6 X-ray Diffraction Results
X-ray diffraction results of Al-Mg/Al2O3 samples were analyzed. The lattice
spacing, d, obtained were compared with standard values of Al, Mg, Al-Mg, Mg-O and
Al-O systems. The presence of various phases was identified and the results of this
analysis are shown in Table 4-14. The XRD spectrums can be found in Appendix C.
Table 4-14
Phase III results of X-ray diffraction analysis.
Al-1.6Mg/Al2O3
Al
5[3]
Number of Matching Peaks
Mg
3[2]
Al12Mg17
-
Al-2.9Mg/Al2O3
5[3]
3[2]
1[1]
Al-3.4Mg/Al2O3
5[3]
3[2]
1[1]
Specimen
[ ] Represents the number of strongest peaks matched.
4.2.7 Mechanical Characterization
4.2.7.1 Hardness
Phase III results of the microhardness and macrohardness measurements (See
Table 4-15) conducted on extruded composite samples revealed an increase in
hardness when magnesium content of the composite is increased.
Table 4-15
Phase III results of hardness test.
Al-1.6Mg/Al2O3
Microhardness
(HV)
66.0 ± 2.6
Macrohardness
(HR15T)
67.3 ± 1.3
Al-2.9Mg/Al2O3
77.0 ± 2.3
71.7 ± 0.6
Al-3.4Mg/Al2O3
78.4 ± 1.8
73.2 ± 1.5
Specimen
53
Results
4.2.7.2 Tensile Properties
The results of ambient temperature tensile test for Phase III are shown in Table
4-16. The tensile test curves are found in Appendix G. The results revealed that an
increase in magnesium/alumina content led to an increase in elastic modulus, 0.2% YS
and UTS of the composite while the failure strain was adversely affected.
Table 4-16
Phase III results of ambient temperature tensile test.
Al-1.6Mg/Al2O3
Modulus
(GPa)
71
0.2% YS
(MPa)
231 ± 6
UTS
(MPa)
264 ± 6
Failure Strain
(%)
8.7 ± 0.5
Al-2.9Mg/Al2O3
73
272 ± 4
350 ± 26
6.1 ± 1.1
Al-3.4Mg/Al2O3
75
302 ± 3
363 ± 25
6.6 ± 0.6
Specimen
4.2.8 Fractography
The tensile fracture surfaces of samples from Phase III are shown in Figure 4-8.
Figure 4-9 shows SEM micrographs at higher magnifications showing the typical
deformation of samples. The fracture surfaces show elongated dimples, indicative of
ductile fracture involving shear stress components. The presence of dimples decreases
and is replaced with striations when the magnesium content is increased. At low
magnifications, the fracture surfaces are all approximately in a plane 45° to the tensile
axis.
54
Results
(a)
(b)
(c)
Figure 4-8
Representative SEM micrographs showing the fracture surface of: (a)
Al-1.6Mg/Al2O3, (b) Al-2.9Mg/Al2O3 and (c) Al-3.4Mg/Al2O3.
55
Results
(a)
(b)
(c)
Figure 4-9
Representative SEM micrographs at high magnification showing the
deformation characteristics of: (a) Al-1.6Mg/Al2O3, (b) Al-2.9Mg/Al2O3
and (c) Al-3.4Mg/Al2O3.
56
Results
4.2.9 Thermal Mechanical Analysis
The thermal mechanical analysis revealed that the average CTE of the samples
decreased when the magnesium/alumina content of the composite is increased (See
Table 4-17).
Table 4-17
Phase III results of thermal mechanical analysis.
Al-1.6Mg/Al2O3
CTE
(x 10-6K-1)
27.12 ± 0.91
Al-2.9Mg/Al2O3
26.50 ± 0.85
Al-3.4Mg/Al2O3
25.44 ± 0.89
Specimen
57
Results
4.3
Phase IV Results
The primary aim of Phase IV was to select the best composite formulation
obtained in Phase III and to study the effect of length scale of the reinforcement on the
properties of Al-Mg metallic matrix. It may be noted that all other processing
parameters were kept the same.
4.3.1 Processing
Macrostructural characterization conducted on the as-cast samples did not
reveal any presence of macropores. Solidification shrinkage cavity was present in all
the as-cast ingots. Following extrusion, there was no evidence of any macrostructural
defects.
The results from the Phase IV extrusion process conducted at an extrusion
temperature of 250°C and ratio of 20.25:1 revealed a decrease in extrusion load when
alumina particulate size is increased (See Table 4-19).
4.3.2 Quantitative Assessment of Reinforcement
The results of image analysis on composite samples in Phase IV revealed an
increase in amount of alumina incorporation in the matrix when the alumina particulate
size is increased. The results are shown in Table 4-18.
58
Results
Table 4-18
Phase IV results of quantitative assessment of Mg and Al2O3 in
composites.
Specimen
Al-Mg
Al2O3 content
(vol. %)
(wt. %)
-
Mg content
(wt. %)
3.79
Al-Mg-0.05µm Al2O3
0.94
1.40
3.42
Al-Mg-0.3µm Al2O3
1.47
2.18
3.87
Al-Mg-1µm Al2O3
1.59
2.36
3.91
Al-Mg-10µm Al2O3
10.13
14.46
4.07
4.3.3 Quantitative Assessment of Alloying Element
Results of inductively coupled plasma spectrometer on composite samples in
Phase IV showed the successful retention of magnesium in the extruded composite
matrix. The results are shown in Table 4-18.
4.3.4 Density Measurement
The results of density and porosity measurements for Phase IV are shown in
Table 4-19. The volume fraction of porosity was measured using image analysis
conducted on 15 representative SEM micrographs. The results indicate that near dense
Al-Mg/Al2O3 materials can be obtained using the fabrication methodology adopted in
the present study.
59
Results
Table 4-19
Phase IV results of density and porosity measurements, and extrusion
load used.
Al-Mg
Experimental
Density
(gcm-3)
2.641 ± 0.005
Al-Mg-0.05µm Al2O3
2.662 ± 0.009
0.114
130
Al-Mg-0.3µm Al2O3
2.646 ± 0.010
0.041
120
Al-Mg-1µm Al2O3
2.647 ± 0.005
0.021
120
Al-Mg-10µm Al2O3
2.657 ± 0.002
1.033
110
Specimen
Porosity
(vol. %)
Load
(tons)
0.056
100
4.3.5 Microstructural Characterization
Figure 4-10 shows representative SEM micrographs showing grain morphology
of Al-Mg/Al2O3 materials processed in Phase IV. The grain morphology of the matrix
was generally equiaxed. The size and aspect ratio of the grains of the extruded samples
from Phase IV are shown in Table 4-20.
Table 4-20
Phase IV results of quantitative microstructural characterization.
Grain Morphology
Size
Aspect Ratio
(µm)
0.8 ± 0.1
1.3 ± 0.2
Al2O3 Particulates Morphology
Size
Aspect Ratio
(µm)
-
Al-Mg-0.05µm Al2O3
0.4 ± 0.1
1.3 ± 0.2
0.050 ± 0.024
1.6 ± 0.5
Al-Mg-0.3µm Al2O3
0.5 ± 0.1
1.4 ± 0.3
0.304 ± 0.152
1.5 ± 0.3
Al-Mg-1µm Al2O3
0.6 ± 0.1
1.4 ± 0.3
1.087 ± 0.290
1.8 ± 0.6
Al-Mg-10µm Al2O3
0.7 ± 0.1
1.3 ± 0.2
8.032 ± 1.226
1.4 ± 0.2
Specimen
Al-Mg
60
Results
Figure 4-11 shows representative SEM micrographs showing the presence of
uniformly distributed, micron-sized Al12Mg17.
The results of SEM study also revealed the presence of porosity and alumina
clusters (See Figure 4-12). The clustering tendency was found to be greatest in the case
of 10µm alumina reinforcement. As a consequence of this clustering tendency, the
clusters-associated porosity similarly increased in this specimen. Figure 4-13 shows a
magnified view of a cluster and good reinforcement-matrix interfacial integrity.
(a)
(b)
(c)
Figure 4-10
(d)
Representative SEM micrographs showing grain morphology of: (a) AlMg, (b) Al-Mg-0.3µm Al2O3, (c) Al-Mg-1µm Al2O3 and (d) Al-Mg-10µm
Al2O3 samples.
61
Results
(a)
(b)
(c)
(d)
Figure 4-11
Representative SEM micrographs showing uniform distribution of
intermetallic Al12Mg17 (indicated by arrows) in: (a) Al-Mg, (b) Al-Mg0.3µm Al2O3, (c) Al-Mg-1µm Al2O3 and (d) Al-Mg-10µm Al2O3 samples.
62
Results
(a)
(b)
(c)
Figure 4-12
Representative SEM micrographs showing distribution of alumina in:
(a) Al-Mg-0.3µm Al2O3, (b) Al-Mg-1µm Al2O3 and (c) Al-Mg-10µm Al2O3
samples.
63
Results
Figure 4-13
Representative SEM micrograph showing alumina cluster and good
interfacial integrity between individual Al2O3 particulates and matrix in
the case of Al-Mg-10µm Al2O3.
4.3.6 X-ray Diffraction Results
X-ray diffraction results of Al-Mg and Al-Mg/Al2O3 samples were analyzed.
The lattice spacing, d, obtained were compared with standard values of Al, Mg, AlMg, Mg-O and Al-O systems. The presence of various phases was identified and the
results of this analysis are shown in Table 4-21. The XRD spectrums can be found in
Appendix C.
Table 4-21
Specimen
Phase IV results of X-ray diffraction analysis.
Number of Matching Peaks
Mg
Al12Mg17
3[2]
1[1]
Al-Mg
Al
5[3]
Al-Mg-0.3µm Al2O3
5[3]
3[2]
1[1]
-
Al-Mg-1µm Al2O3
5[3]
3[2]
1[1]
-
Al-Mg-10µm Al2O3
5[3]
3[2]
-
2[1]
[ ] Represents the number of strongest peaks matched.
64
Al2O3
-
Results
4.3.7 Mechanical Characterization
4.3.7.1 Hardness
Phase IV results of the microhardness and macrohardness measurements (See
Table 4-22) conducted on extruded samples revealed a decrease in hardness when the
size of alumina particulates is increased. When compared to the hardness of pure
aluminium processed with the same extrusion parameters, the results also show that
the increase in hardness can be attributed to both the presence of magnesium and
alumina.
Table 4-22
Al250a
Microhardness
(HV)
41.3 ± 1.5
Macrohardness
(HR15T)
51.0 ± 1.3
Al-Mg
68.0 ± 2.8
67.4 ± 1.1
Al-Mg-0.05µm Al2O3
78.4 ± 1.8
73.2 ± 1.5
Al-Mg-0.3µm Al2O3
74.1 ± 3.1
69.1 ± 1.1
Al-Mg-1µm Al2O3
73.0 ± 1.5
67.1 ± 0.9
71.2 ± 4.2
62.8 ± 2.7
Specimen
a
Phase IV results of hardness test.
Al-Mg-10µm Al2O3
results reproduced for comparison purposes
4.3.7.2 Tensile Properties
The results of ambient temperature tensile test for Phase IV are shown in Table
4-23. The tensile test curves are found in Appendix G. The results revealed that the
0.2% YS, UTS and failure strain increased when alumina particulate size is decreased.
The failure strain however, starts to decrease when alumina particulate size is reduced
from 0.3µm to 0.05µm.
65
Results
Table 4-23
Phase IV results of ambient temperature tensile test.
Al250a
Modulus
(GPa)
71
0.2% YS
(MPa)
132 ± 2
UTS
(MPa)
137 ± 2
Failure Strain
(%)
19.4 ± 0.6
Al-Mg
70
219 ± 8
320 ± 9
11.8 ± 0.8
Al-Mg-0.05µm Al2O3
75
302 ± 3
363 ± 25
6.6 ± 0.6
Al-Mg-0.3µm Al2O3
73
233 ± 4
342 ± 7
11.1 ± 1.0
Al-Mg-1µm Al2O3
72
230 ± 18
332 ± 9
8.3 ± 1.1
Al-Mg-10µm Al2O3
70
229 ± 13
298 ± 7
5.2 ± 1.0
Specimen
a
results reproduced for comparison purposes
4.3.8 Fractography
The tensile fracture surfaces of samples from Phase IV are shown in Figure
4-14. Figure 4-15 shows SEM micrographs at higher magnifications showing the
typical deformation of samples. At low magnifications, the fracture surfaces are all
approximately in a plane 45° to the tensile axis.
66
Results
(a)
(b)
(c)
(d)
Figure 4-14
Representative SEM micrographs showing the fracture surface of: (a)
Al-Mg, (b) Al-Mg-0.3µm Al2O3, (c) Al-Mg-1µm Al2O3 and (d) Al-Mg10µm Al2O3 samples.
67
Results
Figure 4-15
(a)
(b)
(c)
(d)
Representative SEM micrographs at high magnification showing the
deformation characteristics of: (a) Al-Mg, (b) Al-Mg-0.3µm Al2O3, (c)
Al-Mg-1µm Al2O3 and (d) Al-Mg-10µm Al2O3 samples.
68
Results
4.3.9 Thermal Mechanical Analysis
The thermal mechanical analysis revealed that the average CTE of the
composite samples was lower than the monolithic samples (See Table 4-24). However,
no clear relation between alumina particulate size and the reduction of CTE was
observed.
Table 4-24
Phase IV results of thermal mechanical analysis.
Al-Mg
CTE
(x 10-6K-1)
27.59 ± 0.65
Al-Mg-0.05µm Al2O3
25.44 ± 0.89
Al-Mg-0.3µm Al2O3
26.81 ± 0.25
Al-Mg-1µm Al2O3
26.52 ± 1.23
Al-Mg-10µm Al2O3
24.19 ± 0.38
Specimen
69
Chapter 5: Discussion
Chapter 5
Discussion
5.1
Phase I & II Discussion
5.1.1 Processing
Synthesis of monolithic Al was successfully accomplished using the method of
DMD followed by hot extrusion. Important features revealed in the present study are:
(a) minimal oxidation of aluminium, (b) absence of macropores and blowholes, and (c)
no detectable reaction between Al melt and the graphite crucible.
The minimal oxidation of aluminium during melting and casting suggests that
the experimental arrangement used in this study did not permit the ingress of
air/oxygen. The absence of reaction between the melt with the graphite crucible
suggests that the temperature and time condition used during the synthesis process
were not sufficient to trigger the reaction between the two. The absence of blowholes
and macropores indicates that good solidification conditions were realized in the
metallic mould and also suggests that the continuous flow of argon during the melting
and casting process did not lead to the entrapment of gases even while stirring. These
results indicate the feasibility of the DMD process as a fabrication technique for
aluminium.
5.1.2 Secondary processing
The results from the Phase I & II extrusion process showed that the extrusion
load increased as extrusion temperature was decreased or extrusion ratio was increased
(See Table 4-1 and Table 4-2). This can be attributed to an increase in resistance to
plastic deformation. The scientific principles for such behavior are widely established
and will not be discussed here [18].
71
Discussion
5.1.3 Density and Porosity
The density measurement for each specimen was carried out using 3 different
samples at different sections of the extruded rods. From the results obtained (See Table
4-1 and Table 4-2), the standard deviations in all the cases were low. This indicates
homogeneity of microstructural features throughout the extruded rods. From the
density measurements, the porosity values were calculated and the porosity levels
found in all the specimens were small and of similar values (See Table 4-1 and Table
4-2). The presence of minimal porosity in the aluminium samples can be attributed to:
(a) realization of good solidification conditions during the deposition stage and (b) the
use of an appropriate extrusion ratio. It has been established convincingly in earlier
studies that an extrusion ratio as low as 12:1 is able to nearly close the micrometer-size
porosity associated with as-solidified metal-based materials [3, 28, 31]. These results
also revealed that there was no significant impact of extrusion temperature or extrusion
ratio used in the present study on the porosity of the aluminium materials investigated.
5.1.4 Microstructure
The relatively finer grain size exhibited by aluminium as the extrusion
temperature is reduced can be attributed to less grain growth at lower temperatures
(See Table 4-3). With the decrease in extrusion temperature used, there is less energy
for grain growth to occur, resulting in a smaller recrystallized grain structure. Finer
grain size of aluminium is also observed when the extrusion ratio is increased. This
can be attributed to the larger deformation the material is subjected to as the extrusion
ratio is increased. This larger deformation has the ability to lower the recrystallization
temperature, thus increasing the extent of recrystallization, thereby resulting in finer
grains.
72
Discussion
5.1.5 Mechanical Behavior
The results of hardness measurements revealed that lowering the extrusion
temperature or increasing the extrusion ratio led to an increase in the average
microhardness and the overall bulk hardness of aluminium (See Table 4-5 and Table
4-6). This can be attributed to the progressively refined grain size. Strengthening due
to grain boundaries results from mutual interference to slip within grains [18]. When
the grain size is reduced, it implies that there is an increase in grain boundary area,
thereby increasing strength.
The results of the tensile properties revealed no significant change in the elastic
modulus (See Table 4-7 and Table 4-8) with changes in the extrusion temperature or
ratio. The elastic modulus is one of the most structure-insensitive of the mechanical
properties. It is only slightly affected by alloying or reinforcement additions, heat
treatment, or cold work [32].
The results revealed an increase in 0.2% offset yield stress (0.2% YS) and
ultimate tensile stress, and a reduction of ductility when the extrusion temperature is
decreased or extrusion ratio is increased (See Table 4-7 and Table 4-8). Similar results
have been reported by other investigators [33]. This can be attributed primarily to the
reduction in matrix grain size and to the strain hardening for samples extruded below
recrystallization temperature. The grain-size dependence of yield stress and other
properties in metals has been established by the pioneering work of Hall [34] and
Petch [35].
σ 0 = σ i + kD
−
1
2
… (1)
where σ0 is the yield stress, σi is the friction stress needed to move individual
dislocations, k is a “locking parameter” which measures the relative hardening
73
Discussion
contribution of grain boundaries, and D is the average grain size. In the case of
aluminium, the Hall-Petch slope is low. Hence, only moderate improvement in yield
stress can be expected with grain refinement.
The original explanation for this effect was that dislocation pile-ups formed at
grain boundaries and required a critical stress to break through them. Grain boundaries
thus act as barriers to dislocation motion and hence increase the yield stress. An
alternative model was proposed by Li [36] and Conrad [37], which related the grain
size effects to dislocation density instead of the pile-up explanation. Research has
shown that grain boundaries themselves also serve as dislocation sources. The
dislocation density explanation was thus formulated and it is a model that does not
emphasize on stresses at grain boundaries. It is a more general model that relates the
grain size to dislocation density, which in turn affects the yield stress. The grain size
effect has been verified by investigators in numerous studies involving aluminium
alloys [38] and magnesium composites [39].
In addition to grain size effects, the increase in properties can also be attributed
to the breaking up of columnar and other unfavorable crystal arrangements which tend
to generate points of weakness along particular planes and directions [40]. By the
nature of extrusion, the outer zones of an extruded bar will undergo greater
deformation than the centre. This will create a difference in the properties between
these regions, the variation being greatest when the extrusion ratio is low. Hence, a
higher extrusion ratio will produce a bar with more uniform and improved properties.
Considering hardness (indicative of wear resistance), 0.2% YS and UTS (basis
of strength-based designs) as the important properties from a design engineer’s
perspective, extruding aluminium at 85°C with an extrusion ratio of 26.45:1 should
result in the best combination of mechanical properties (See Table 4-23).
74
Discussion
5.1.6 Fractography
The results of fracture surface analysis revealed the presence of dimples,
indicative of ductile fracture in all cases. An increase in extrusion temperature or
decrease in extrusion ratio resulted in smaller dimples (See Figure 4-3 and Figure 4-4).
This feature can primarily be attributed to the refining of the grain structure.
5.1.7 Thermal Mechanical Analysis
The results of CTE measurements did not reveal any correlation with extrusion
temperature and ratio. This indicates that the microstructural variation obtained by
variation of these variables was not sufficient to change CTE of the aluminium.
5.1.8 Proceeding to Phase III
The above results revealed that extruding aluminium at 85°C with an extrusion
ratio of 26.45:1 will realize the best mechanical properties. Thus, it was decided to
process the samples in Phase III and IV with these extrusion parameters. Several
attempts were made for the composite formulations but the samples could not be
extruded due to limitations of the press capacity. By attempting a number of trials with
the next best combination of extrusion parameters, successful extrusions with
composite formulations were made at an extrusion temperature of 250°C and extrusion
ratio of 20.25:1.
75
Discussion
5.2
Phase III Discussion
5.2.1 Processing
Synthesis of Al-Mg/Al2O3 materials was successfully accomplished using the
method of DMD followed by hot extrusion. Important features revealed in the present
study are: (a) minimal oxidation of aluminium, (b) absence of macropores and
blowholes, and (c) no detectable reaction between Al-Mg melts and the graphite
crucible.
The minimal oxidation of Al-Mg during melting and casting suggests that the
experimental arrangement used in this study did not permit the ingress of air/oxygen.
The absence of reaction between the melt with the graphite crucible suggests that the
temperature and time condition used during the synthesis process were not sufficient to
trigger the reaction. The absence of blowholes and macropores indicates that good
solidification conditions were realized in the metallic mould and also suggests that the
continuous flow of argon during the melting and casting process did not lead to the
entrapment of gases even while stirring. These findings are similar to that in Phase I
and II and suggest that addition of Mg to Al did not adversely affect the solidification
processing.
The results of image analysis conducted on extruded samples from Phase III
revealed successful incorporation of up to 1.4 wt. % of alumina particulates in the AlMg melt. The incorporation of alumina increases when the magnesium content of the
Al matrix increases. This can be attributed to the ability of magnesium to function as a
wetting reagent. Existing literature [41] has shown that magnesium aids in the wetting
of alumina particulates in an aluminium matrix and also reduces agglomeration of
particulates. These results indicate the feasibility of the DMD process as a fabrication
technique for Al-Mg/Al2O3 MMCs.
76
Discussion
5.2.2 Secondary processing
The results from the Phase III extrusion process showed that the extrusion load
increased as the magnesium/alumina content of the aluminium matrix increased. A
near linear fit was obtained with extrusion load and the cumulative magnesium and
alumina reinforcement weight percent (See Figure 5-1). This can be attributed to an
increase in resistance of the material to plastic deformation which occurs due to
precipitation hardening of secondary phases and the incorporation of more alumina
reinforcement.
140
EL (Extrusion Load, Tons)
120
EL = 12.339W + 69.433
R = 0.999
100
80
60
40
20
0
0
1
2
3
4
5
6
W (Mg + Al2O3, wt.%)
Figure 5-1
Graph of extrusion load vs. cumulative magnesium and alumina
reinforcement weight percent.
5.2.3 Density
The density measurement for each specimen was carried out using 3 different
samples at different sections of the extruded rods. From the results obtained (See Table
4-12), the standard deviation in all the cases were low. This indicates a uniform
composition realized throughout the extruded rods.
77
Discussion
5.2.4 Microstructure
The results of the microstructural characterization studies conducted on the
extruded Al-Mg/Al2O3 samples are discussed in terms of: (a) size and distribution of
reinforcement in the composite, (b) reinforcement-matrix interfacial characteristics, (c)
grain morphology, and (d) the presence of porosity.
The results of field emission scanning electron microscopy revealed a uniform
distribution of alumina particulates with an average size of around 50nm (See Table
4-13). The absence of alumina peaks in XRD results can be attributed to the inability
of filtered X-ray radiation to detect phases with less than 2 volume percent in a
multiphase structure [42]. SEM micrographs also show the presence of a uniformly
distributed secondary phase, Al12Mg17. The XRD results support the formation of this
intermetallic phase. The uniform distribution of alumina reinforcement realized in the
present study can be attributed to: (a) limited agglomeration of reinforcement due to
proper selection of reinforcement feed rate, (b) minimal gravity-associated segregation
due to the judicious selection of stirring parameters, (c) good wetting (as evidenced
from good Al2O3/Al-Mg interface) of reinforcement by the matrix melt [43], and (d)
disintegration of the composite slurry by argon jets into droplets, and its subsequent
deposition in the metallic mold.
The interface is characterized by the reaction at the interface and the interface
strength. From the XRD results, no reaction phase was detected in all the cases. The
two possible reactions at the interface between magnesium and alumina are listed
below [44]:
3Mg + Al2O3 = 2Al + 3MgO
… (2)
3Mg + 4Al2O3 = 2Al + 3MgAl2O4
… (3)
78
Discussion
Neither MgAl2O4 nor MgO were detected, indicating that the reactions did not
occur or that the reaction at the interface was minimal. The interfacial integrity
appeared to be good as observed using the FESEM but TEM studies may be required
for detailed characterization due to the nanometric size of the alumina. From the good
mechanical properties displayed by the materials investigated in Phase III, it can be
assumed that the interface formed between reinforcement and matrix was good. This
indicates that the temperature and time conditions selected during processing permitted
good compatibility between the Al-Mg matrix and alumina reinforcement.
There is no significant change in grain size exhibited by the aluminium matrix
as the magnesium/alumina content is changed. There is however, a significant
reduction in grain size from 12-23µm to 0.4-0.8µm when compared to the aluminium
materials investigated in Phases I & II (See Tables 4-3, 4-4 and 4-20). This reduction
in grain size can be attributed to both the Zener pinning effect [45] of nanosized
alumina particulates and particulate stimulated nucleation (PSN) [46] from the alumina
particulates and the micron-sized eutectic Al12Mg17 that forms due to the addition of
magnesium into aluminium.
The presence of minimal porosity in Al-Mg/Al2O3 composite materials (See
Table 4-12) can be attributed to: (a) realization of good solidification conditions during
the deposition stage, (b) good compatibility between the Al-Mg matrix and Al2O3
particulates during solidification leading to the absence of voids and debonded regions
normally associated with the reinforcement-matrix interface, and (c) the use of an
appropriate extrusion ratio. It has been established convincingly in earlier studies that
an extrusion ratio as low as 12:1 is able to nearly close the micrometer-size porosity
associated with as-solidified metal-based materials [3, 28, 31]. These results also
79
Discussion
revealed that there was no significant impact of magnesium/alumina content of the
aluminium matrix on the porosity of the materials investigated.
5.2.5 Mechanical Behavior
The results of hardness measurements revealed that increasing the
magnesium/alumina content led to an increase in the average microhardness and the
overall bulk hardness of the composite (See Table 4-15). This can be attributed to: (a)
increased incorporation of hard alumina particulates, (b) increased formation of brittle
intermetallic Al12Mg17 phases [47] in the matrix, and (c) a higher constraint to the
localized matrix deformation during indentation due to their presence. These results
are consistent with similar findings obtained on Al/SiC composite materials [48].
The elastic modulus measurement revealed that an increase in the magnesium
content led to an increase in the elastic modulus of the composite (See Table 4-16).
Increase in modulus was expected due to: (a) increasing presence of stiffer alumina
and Al12Mg17, and (b) uniform distribution of reinforcement with good interfacial
integrity. The uniform distribution of reinforcement coupled with good matrixreinforcement interfacial integrity enables effective load transfer from the matrix to the
reinforcement. This generates a significant increase in internal stress between
reinforcement and matrix, resulting in the enhancement of the elastic modulus.
The results of tensile properties characterization revealed that the 0.2% YS and
UTS of the composite samples increased when the magnesium/alumina content is
increased. A linear trend was observed in both properties with respect to the
cumulative magnesium/alumina content (See Figure 5-2 and Figure 5-3). This
substantial improvement of strength can be attributed to the increasing amounts of
uniformly distributed alumina particulates and Al12Mg17 intermetallics. This
80
Discussion
observation of increased strength with increasing alumina incorporation and alloying
content is in line with the concept that the strength of particle reinforced composites is
dependant on the volume fraction of reinforcement/alloying elements [3]. Due to the
nanometric size of the alumina particulates, Orowan strengthening can be a major
factor in the increase in strength. Further strengthening of the aluminium matrix is
produced by precipitation hardening of the Al12Mg17 phase. Similar results are
observed by other researchers [49]. It is found that the hardening kinetics is enhanced
by Al2O3 particulates because the precipitation preferentially develops on the
dislocation lines that increased due to coefficient of thermal expansion mismatch
between the matrix and reinforcement. It must be noted that the presence of
reinforcement did not change the precipitation characteristics of the investigated
composites.
350
YS = 30.713W + 150.22
R = 0.998
300
YS (0.2% YS, MPa)
250
200
150
100
50
0
0
1
2
3
4
5
W (Mg + Al2O3, wt.%)
Figure 5-2
Graph of 0.2% YS vs. cumulative magnesium and alumina
reinforcement weight percent.
81
6
Discussion
450
400
350
UTS = 44.652W + 154.29
R = 0.997
UTS, MPa
300
250
200
150
100
50
0
0
1
2
3
4
5
6
W (Mg + Al2O3, wt.%)
Figure 5-3
Graph of UTS vs. cumulative magnesium and alumina reinforcement
weight percent.
The ductility of composites decreased with increasing magnesium/alumina
content. The reduction in ductility can be attributed to the reduced cavitation resistance
of the metallic matrix due to the presence of brittle alumina particulates and
intermetallic phases in the matrix [50, 51].
5.2.6 Fractography
The striations observed in the micrographs (See Figure 4-8 and Figure 4-9) are
the results of dislocation slip steps formed by plastic deformation after void formation.
The extent of striations increased with an increase in magnesium/alumina content.
Thus, the micrographs support the observation of lowered ductility with an increase in
magnesium/alumina content.
5.2.7 Coefficient of Thermal Expansion (CTE)
The results of CTE measurements in the temperature range of 50-400°C
revealed that the increase in magnesium/alumina content in the matrix reduced the
82
Discussion
CTE of the composite (See Table 4-17). The CTE of magnesium is marginally more
than that of aluminium so the addition of magnesium should contribute to increasing
the CTE of the composite. However, the increase in magnesium content of the matrix
led to an increase in alumina incorporation and precipitation products in the matrix.
Hence, the reduced CTE of the composite can be attributed to the lower CTE of
alumina and Al-Mg secondary phases.
5.2.8 Proceeding to Phase IV
The above results revealed that adding 3.4 wt. % Mg to aluminium will realize
the maximum incorporation of alumina and hence the best improvement in mechanical
properties. Thus, it was decided to fabricate the composites in Phase IV with the
addition of 3.4 wt. % of magnesium. It may be noted that the main aims of Phase IV
was to investigate the effect of length scale of the reinforcement on the microstructure
and properties of Al-Mg matrix.
83
Discussion
5.3
Phase IV Discussion
The main aim of Phase IV was to investigate the effect of length scale of
alumina reinforcement on the microstructure and properties of Al-3.4Mg metallic
matrix.
5.3.1 Processing
Synthesis of Al-Mg/Al2O3 materials was successfully accomplished using the
method of DMD followed by hot extrusion. Important features revealed in the present
study are: (a) minimal oxidation of aluminium, (b) absence of macropores and
blowholes, and (c) no detectable reaction between Al-Mg melts and the graphite
crucuible. These observations were similar to that discussed in Phases I to III and
hence will not be discussed here.
The results of image analysis conducted on extruded samples from Phase IV
revealed successful incorporation of up to 14.46 wt. % of alumina particulates (Size:
10µm) in the Al-Mg melt. The incorporation of alumina increases when the alumina
particulate size increases. This can be attributed to the better wetting of coarser
particles [3].
5.3.2 Secondary Processing
The results from Phase IV extrusion process showed that the extrusion load
increased as the alumina particulate size decreased. This can be attributed to an
increase in resistance of the material to plastic deformation primarily due to a
progressive increase in the strengthening ability of alumina particulates.
84
Discussion
5.3.3 Density
The density measurement for each specimen was carried out using 3 different
samples at different sections of the extruded rods. From the results obtained (See Table
4-19), the standard deviation in all the cases were low. This indicates a uniform
dispersion of alumina particulates and composition in terms of magnesium throughout
the extruded rods.
5.3.4 Microstructure
The results of the microstructural characterization studies conducted on the
extruded Al-Mg/Al2O3 samples are discussed in terms of: (a) size and distribution of
reinforcement in the composite, (b) reinforcement-matrix interfacial characteristics, (c)
grain morphology, and (d) presence of porosity.
The results of scanning electron microscopy revealed the presence of finite
amount of alumina particulate clusters. The occurrence of clusters increases with
increasing volume fraction of alumina particulates. The increase in particulate
clustering and porosity levels with an increase in alumina volume fraction can be
attributed to the combined effects of: (a) the inability of the melt to infiltrate the
micrometer sized crevices in the inefficiently packed ceramic particulate clusters
formed during solidification [28, 52, 53], and (b) the increase in the apparent viscosity
of the aluminium melt, limiting its ability to vent trapped air [28, 54]. Alumina peaks
were absent in all XRD results except for Al-Mg-10µm Al2O3. This can be attributed
to the inability of filtered X-ray radiation to detect phases of less than 2 volume
percent in a multiphase structure [42]. The micrographs of all samples show the
85
Discussion
presence of a uniformly distributed secondary phase, Al12Mg17 (See Figure 4-11). The
XRD results support the formation of this intermetallic phase.
The interfacial integrity of samples Al-Mg-0.3µm Al2O3 and Al-Mg-1µm
Al2O3 could not be determined from the SEM micrographs due to the small size of the
alumina. TEM analysis is recommended to investigate the interfacial integrity. The
results of microstructural characterization of Al-Mg-10µm Al2O3 revealed a near
defect free interface formed between reinforcement and matrix (See Figure 4-13). The
interfacial integrity was assessed in terms of interfacial debonding and presence of
microvoids at the particulate-matrix interface. The results indicate that the temperature
and time conditions selected during the processing permitted good compatibility
between the Al-Mg matrix and alumina reinforcement.
Studies of the grain morphology of samples in Phase IV (See Table 4-20)
revealed a decrease in average grain size when the alumina particulate size is
decreased. This observation shows that the grain size dependence on reinforcement
size is greater than the volume fraction of reinforcement added. Even with a lower
volume fraction of reinforcement and lower grain refinement contribution from a
slightly lower magnesium content, Al-Mg-0.05µm Al2O3 sample possesses a finer
grain structure than Al-Mg-10µm Al2O3.
The porosity levels are similar to the composite materials synthesized in Phase
III with the exception of Al-Mg-10µm Al2O3. The porosity was mostly associated with
alumina clustering hence the increase in porosity levels can be attributed to the
increase in amount of alumina in the matrix. This observation is consistent with the
results of other studies made on MMCs [28].
86
Discussion
5.3.5 Mechanical Behavior
The results of hardness measurements revealed an increase in hardness when
reinforcement size is decreased (See Table 4-22). This can be attributed to the
progressively refined matrix grain size and better distribution of reinforcement as
reinforcement size is decreased [24]. It may be noted that the macrohardness of AlMg-10µm Al2O3 is lower than that of monolithic Al-Mg. This can be attributed to the
presence of high porosity in Al-Mg-10µm Al2O3 samples.
The elastic modulus measurement revealed that an increase in the
reinforcement size led to a decrease in the elastic modulus (See Table 4-23). This can
be attributed to the improved distribution of alumina particulates when the
reinforcement size is decreased. The absence of precipitation products in the Al-Mg10µm Al2O3 samples can also explain the low elastic modulus of the composite. More
studies must be done to ascertain the extent of precipitation hardening in all samples
and its effect on the elastic modulus.
The increase in 0.2% YS and UTS with a decrease in alumina particulate size
(See Table 4-23) can be attributed to: (a) the reduction in matrix grain size, (b)
increased dislocation density [24] and (c) an increase in strengthening ability of
alumina particulates. The influence of matrix grain size on the yield strength has
already been discussed earlier in Phase I & II. It is suggested that smaller sized
particulates are more effective at increasing the average dislocation density and hence,
the magnitude of residual stress state. The effect of reinforcement size is shown to be
more dominant than the effect of volume fraction of reinforcement. The high volume
fraction of alumina reinforcement in Al-Mg-10µm Al2O3 has the lowest mechanical
properties of the composites investigated in this study. The low yield strength in the
case of Al-Mg-10µm Al2O3 can also be attributed to the minimization of precipitation
87
Discussion
hardening as can be seen by the absence of Al12Mg17 intermetallic (See Table 4-21).
The minimization in precipitation hardening can be attributed to the increase in
interfacial reactions between Al-Mg and Al2O3 as a result of higher volume fraction of
alumina particulates. The increased interfacial reaction will lead to increased
magnesium depletion from the matrix, and hence less formation of Al12Mg17. The
absence of Al12Mg17 peaks in the XRD results (See Table 4-21) supports this
explanation. Similar results have been reported by other investigators [55]. The results
indicate that the strengthening mechanisms triggered by the particles up to 0.3µm size
were not capable of influencing strength of the matrix. As the particle size further
reduces, Orowan strengthening mechanisms are likely to initiate and responsible for
the jump in 0.2% YS. Orowan strengthening is a mechanism in which the yield stress
is determined by the shear stress required to bow a dislocation line between 2 particles.
12
380
360
10
340
8
300
6
280
260
Ductility (%)
Stress (MPa)
320
0.2% YS
UTS
Ductility
4
240
2
220
200
0.01
0
0.1
1
10
Reinforcement Size (µm)
Figure 5-4
Graph of 0.2% YS, UTS and ductility vs. alumina particulate size.
There exists a parabolic relationship between alumina particulate size and
ductility. A reduction in particulate size from 10µm to 0.3µm increases the ductility.
Further reduction of particulate size to 0.05µm decreases the ductility. Similar results
88
Discussion
have been reported by other investigators using SiC as reinforcement [24]. The results
thus indicate that there exists a threshold in alumina particulate size up to which
ductility improves and beyond which it deteriorates. Increasing cavitation resistance
and clustering tendency of particulates work in opposition to each other as the
particulate size is decreased. Ductility will first show an increasing trend with
decreasing particulate size because increased cavitation resistance has a more
pronounced effect than the loss of ductility due to increasing clustering. Once a
threshold particulate size is reached, ductility will start to decrease as the contribution
from particulate clustering is more than that from increased cavitation resistance.
The results of the present study indicate that the strength of Al-Mg/Al2O3
composites can be increased more effectively by reducing the reinforcement particle
size than by increasing its volume fraction (See Figure 5-5). The use of 0.05µm
alumina particulates increased overall mechanical properties without severe
detrimental effect on ductility. This study thus shows great potential for use of AlMg/Al2O3 composites containing nanosize alumina particulates in strength-critical
applications.
400
350
300
250
200
150
100
50
0
Modulus (GPa)
Figure 5-5
0.2% YS (MPa)
UTS (MPa)
Al250
Al-Mg
Al-1.6Mg/Al2O3
Al-2.9Mg/Al2O3
Al-3.4Mg/Al2O3 (Al-Mg-0.05 micron Al2O3)
Al-Mg-0.3 micron Al2O3
Al-Mg-1 micron Al2O3
Al-Mg-10 micron Al2O3
Failure Strain (%)
Bar chart showing a summary of mechanical properties of materials fabricated
in the present study.
89
Discussion
5.3.6 Fractography
The results of fracture surface analysis indicated the ductile mode of failure of
the Al-Mg matrix. The dimples in all the cases were slightly elongated, indicative of
shear stress component during tensile fracture (See Figure 4-15). Presence of big,
crater-like area was observed in the case of Al-Mg-10µm Al2O3 and can be attributed
to the presence of Al2O3 clusters. The results also indicated a progressive increase in
the flat and featureless area on the fracture surface of the samples with progressive
decrease in the alumina particulate size. This can be attributed to the increasing brittle
fracture due to a decrease in alumina particulate size. This observation was very clear
for the Al-Mg-0.05µm Al2O3 samples and is supported by the results presented in
Table 4-23.
5.3.7 Coefficient of Thermal Expansion (CTE)
The results of CTE measurements (See Table 4-24) in the temperature range of
50-400°C revealed that the addition of alumina reinforcement reduced the CTE of the
composite. The CTE reduction is greatest for Al-Mg-10µm Al2O3 due to the high
volume fraction of alumina incorporated. The results do indicate that CTE reductions
per unit volume percent of alumina particulates added remains highest in the case of
Al-Mg-0.05µm Al2O3 samples.
90
Chapter 6: Conclusions
Chapter 6
Conclusions
From the results and observations made from microstructural characterization
and mechanical properties of the materials synthesized in this study, the following
conclusions can be made:
Phase I & II
1. The DMD technique coupled with extrusion process (with extrusion
temperature ranging from room temperature to 350°C) can successfully
be used to synthesize aluminium material with low porosity.
2. Grain size measurement conducted indicates that grain size of the
matrix undergoes progressive refinement with a decrease in extrusion
temperature. A similar trend occurs when the extrusion ratio is
increased.
3. Hardness measurement results conducted indicate that the hardness
increases with a decrease in extrusion temperature or an increase in
extrusion ratio.
4. The tensile testing results indicate that the reduction in extrusion
temperature or increase in extrusion ratio leads to an increase in 0.2%
yield strength and UTS, while the ductility was adversely affected. The
elastic modulus remained the same.
92
Conclusions
5. Considering hardness, 0.2% yield strength and UTS as the most
important features from a design engineer’s perspective, extruding
aluminium materials at 85°C with an extrusion ratio of 26.45:1 were
projected to realize the best mechanical properties.
6. Thermal mechanical analysis revealed that the CTE was unaffected by
extrusion temperature or ratio.
Phase III
1. The DMD technique coupled with extrusion process can successfully
synthesize composites of Al-Mg formulations reinforced with 0.05µm
alumina particulates. All materials exhibit low porosity after extrusion.
2. The uniform distribution of alumina particulates and the presence of
minimal porosity in the composite microstructure indicate the suitability
of primary processing and secondary processing parameters used in the
study.
3. Hardness measurement results indicate that the hardness increased with
an increase in magnesium/alumina content.
4. The
tensile
testing
results
indicate
that
an
increase
in
magnesium/alumina content leads to an increase in elastic modulus,
0.2% yield strength and UTS, while the ductility was adversely
affected.
93
Conclusions
5. Considering hardness, elastic modulus, 0.2% yield strength and UTS as
the most important features from a design engineer’s perspective,
adding 3.4 wt.% magnesium to aluminium will realize the best
mechanical properties.
6. Thermal mechanical analysis revealed that an increase in magnesium
content is able to improve the dimensional stability of aluminium. This
can be attributed to a corresponding increase in alumina particulate
incorporation when magnesium content is increased.
Phase IV
1. The DMD technique coupled with extrusion process can successfully
synthesize composites of Al-Mg reinforced with alumina particulates
ranging in size from 0.05µm to 10µm. All materials exhibit low
porosity after extrusion with the exception of materials reinforced with
10µm particulates.
2. The uniform distribution of alumina particulates and the presence of
minimal porosity in the composite microstructure indicate the suitability
of primary processing and secondary processing parameters used in the
study.
3. Hardness measurements conducted indicate that the hardness decreased
with an increase in particulate size.
94
Conclusions
4. The tensile testing results indicate that a decrease in alumina particulate
size leads to an increase in elastic modulus, 0.2% yield strength and
UTS. There exists a parabolic relationship between alumina particulate
size and ductility. Improvement in ductility was realized as alumina
particulate size decreased until a threshold size of 0.3µm.
5. Considering hardness, elastic modulus, 0.2% yield strength and UTS as
the most important features from a design engineer’s perspective,
adding 0.05µm alumina particulates to an Al-Mg matrix will realize the
best mechanical properties.
6. Thermal mechanical analysis revealed that an increase in the presence
of alumina is able to improve the dimensional stability of aluminium.
Considering the volume fraction of alumina particulates incorporated,
the best CTE was obtained in the case of Al-Mg-0.05µm Al2O3
formulation.
95
Chapter 7: Recommendations
Chapter 7
Recommendations
The following are some suggestions for future work in this area:
1. Primary processing parameters should be investigated to obtain higher
incorporation of nanosized alumina.
2. Transmission electron microscopy (TEM) should be used to analyze the
Al-Mg/Al2O3 interface and the reaction product formed.
3. The effect of nanosized alumina addition on precipitation hardening
should be investigated further.
4. Heat treatment studies should be carried out to further improve the
mechanical properties.
5. Nanosized reinforcements of other materials, such as SiC, should be
investigated.
97
References
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Appendix
Appendix
Appendix A: Processing log sheets
General Description
1
Al
Experiment No.
MMC System
16th October 2001
Success
Date
Status
Raw Materials
Material Type
Weight
Weight Percentage
Form
Pre-treatment
Matrix
Al
1500.00g
100%
Granules
-
Reinforcement
-
Heating Temperatures
1545h
Initial Temp.
28 °C
Ending Time
1730h
Final Temp.
Time taken to reach
required temperature
750 °C
900
Temp. (oC)
Starting Time
600
300
0
0
1.75 hrs
60
120
180
Time (mins)
Equipment Parameters
Stirrer Diameter
Stirrer Pretreament
Graphite
A12
105 mm
25.4 mm
Mild Steel , Twin
Blades Pitch 45°
75 mm
Coat with zirtex
Stirring Position
Stirring Temperature
Bottom of melt
750 °C
Crucible Type
Crucible Size
Crucible Diameter
Crucible Hole Diameter
Stirrer Type
Nozzle Type
Nozzle Diameter
Nozzle Hole Diameter
Mould Type
Graphite
25.4 mm
10 mm
Stainless Steel
Mould Pretreatment
Sandpaper and coat with graphite spray
Mould Diameter
Stirrer Clamping Position
40 mm
425 mm from blade
Reinforcement Addition and Stirring
Stirring Speed
Stirring Duration
500 rpm
3 min
Argon Supply
Before Stirring
5 l/min
During Stirring
5 l/min
Melt Disintegration and Deposition Parameters
Disintegrating Gas
Nozzle Diameter
Disintegrating Gas Flow
Rate
Pouring Temperature
Disintegrating Duration
2 nozzles
4 mm diameter
25 l/min
750 °C
8 sec
Initial Weight
Deposited Weight
(after casting)
1500.00g
Deposited Ingot Height
450mm
1450.00g
Deposited Yield %
96.67%
Disintegrating Gas Type
Argon
Disintegrating Gas Pressure
Total Flight Distance
Disintegrating Flight
Distance
150 bar
765 mm
500 mm
Process Percentage Yield
Remarks
Weather – Fair
Shrinkage cavity observed at top of ingot
Appendix
General Description
2
Al/Al2O3
Experiment No.
MMC System
6th December 2001
Unsuccessful
Date
Status
Raw Materials
Material Type
Weight
Weight Percentage
Form
Pre-treatment
Matrix
Al
1500.00g
86%
Granules
-
Reinforcement
Al2O3
162.96g
14%
0.3µm particulates
Preheat at 500°C for 1 hour
Heating Temperatures
1325h
Initial Temp.
30 °C
Ending Time
1515h
Final Temp.
Time taken to reach
required temperature
750 °C
900
Temp. (oC)
Starting Time
600
300
0
0
1.75 hrs
60
120
180
Time (mins)
Equipment Parameters
Graphite
A12
105 mm
25.4 mm
Mild Steel , Twin
Blades Pitch 45°
Nozzle Type
Nozzle Diameter
Nozzle Hole Diameter
Mould Type
Graphite
25.4 mm
10 mm
Stainless Steel
Mould Pretreatment
Sandpaper and coat with graphite spray
Stirrer Diameter
Stirrer Pretreament
75 mm
Coat with zirtex
Mould Diameter
Stirrer Clamping Position
40 mm
425 mm from blade
Stirring Position
Stirring Temperature
Bottom of melt
750 °C
Crucible Type
Crucible Size
Crucible Diameter
Crucible Hole Diameter
Stirrer Type
Reinforcement Addition and Stirring
Sti rring Speed
Stirring Duration
500 rpm
3 min
Argon Supply
Before Stirring
5 l/min
During Stirring
5 l/min
Melt Disintegration and Deposition Parameters
Disintegrating Gas
Nozzle Diameter
Disintegrating Gas Flow
Rate
Pouring Temperature
Disintegrating Duration
2 nozzles
4 mm diameter
25 l/min
750 °C
-
Initial Weight
Deposited Weight
(after casting)
1500.00g
Deposited Ingot Height
-
-
Deposited Yield %
-
Disintegrating Gas Type
Argon
Disintegrating Gas Pressure
Total Flight Distance
Disintegrating Flight
Distance
150 bar
765 mm
500 mm
Process Percentage Yield
Remarks
Weather – Fair
Melt solidifies at the plug, leaving large amounts of melt and alumina powder in the crucible
Appendix
General Description
3
Al/Al2O3
Experiment No.
MMC System
28th December 2001
Unsuccessful
Date
Status
Raw Materials
Material Type
Weight
Weight Percentage
Form
Pre-treatment
Matrix
Al
1000.00g
95.7%
Granules
-
Reinforcement
Al2O3
49.90g
4.3%
0.3µm particulates
Preheat at 500°C for 1 hour
Heating Temperatures
Starting Time
1510h
Initial Temp.
28 °C
Ending Time
1700h
Final Temp.
Time taken to reach
required temperature
750 °C
Crucible Type
Crucible Size
Crucible Diameter
Crucible Hole Diameter
Graphite
A12
105 mm
25.4 mm
Mild Steel , Twin
Blades Pitch 45°
Nozzle Type
Nozzle Diameter
Nozzle Hole Diameter
Mould Type
Graphite
25.4 mm
10 mm
Stainless Steel
Mould Pretreatment
Sandpaper and coat with graphite spray
Stirrer Diameter
Stirrer Pretreament
75 mm
Coat with zirtex
Mould Diameter
Stirrer Clamping Position
40 mm
425 mm from blade
Stirring Position
Stirring Temperature
Bottom of melt
750 °C
Temp. (oC)
900
600
300
0
0
1.8 hrs
60
120
180
Time (mins)
Equipment Parameters
Stirrer Type
Reinforcement Addition and Stirring
Stirring Speed
Stirring Duration
500 rpm
3 min
Argon Supply
Before Stirring
5 l/min
During Stirring
5 l/min
Melt Disintegration and Deposition Parameters
Disintegrating Gas
Nozzle Diameter
Disintegrating Gas Flow
Rate
Pouring Temperature
Disintegrating Duration
2 nozzles
4 mm diameter
25 l/min
750 °C
8 sec
Initial Weight
Deposited Weight
(after casting)
1049.90g
Deposited Ingot Height
-
-
Deposited Yield %
-
Disintegrating Gas Type
Argon
Disintegrating Gas Pressure
Total Flight Distance
Disintegrating Flight
Distance
150 bar
765 mm
500 mm
Process Percentage Yield
Remarks
Large amounts of alumina powder left in the crucible after casting.
Small amount of melt solidified at the plug.
Appendix
General Description
4
Al
Experiment No.
MMC System
25th February 2002
Success
Date
Status
Raw Materials
Material Type
Weight
Weight Percentage
Form
Pre-treatment
Matrix
Al
1500.00g
100%
Granules
-
Reinforcement
-
Heating Temperatures
1230h
Initial Temp.
30 °C
Ending Time
1415h
Final Temp.
Time taken to reach
required temperature
750 °C
900
Temp. (oC)
Starting Time
600
300
0
0
1.75 hrs
60
120
180
Time (mins)
Equipment Parameters
Graphite
A12
105 mm
25.4 mm
Mild Steel , Twin
Blades Pitch 45°
Nozzle Type
Nozzle Diameter
Nozzle Hole Diameter
Mould Type
Graphite
25.4 mm
10 mm
Stainless Steel
Mould Pretreatment
Sandpaper and coat with graphite spray
Stirrer Diameter
Stirrer Pretreament
75 mm
Coat with zirtex
Mould Diameter
Stirrer Clamping Position
40 mm
425 mm from blade
Stirring Position
Stirring Temperature
Bottom of melt
750 °C
Crucible Type
Crucible Size
Crucible Diameter
Crucible Hole Diameter
Stirrer Type
Reinforcement Addition and Stirring
Stirring Speed
Stirring Duration
500 rpm
3 min
Argon Supply
Before Stirring
5 l/min
During Stirring
5 l/min
Melt Disintegration and Deposition Parameters
Disintegrating Gas
Nozzle Diameter
Disintegrating Gas Flow
Pouring Rate
Temperature
Disintegrating Duration
2 nozzles
4 mm diameter
25 l/min
750 °C
8 sec
Initial Weight
Deposited Weight
(after casting)
1500.00g
Deposited Ingot Height
445mm
1448.00g
Deposited Yield %
96.53%
Disintegrating Gas Type
Argon
Disintegrating Gas Pressure
Total Flight Distance
Disintegrating Flight
Distance
150 bar
765 mm
500 mm
Process Percentage Yield
Remarks
Weather – Fair
Shrinkage cavity observed at top of ingot
Appendix
General Description
5
Al
Experiment No.
MMC System
1st March 2002
Success
Date
Status
Raw Materials
Material Type
Weight
Weight Percentage
Form
Pre-treatment
Matrix
Al
1500.00g
100%
Granules
-
Reinforcement
-
Heating Temperatures
1400h
Initial Temp.
30 °C
Ending Time
1545h
Final Temp.
Time taken to reach
required temperature
750 °C
900
Temp. (oC)
Starting Time
600
300
0
0
1.75 hrs
60
120
180
Time (mins)
Equipment Parameters
Graphite
A12
105 mm
25.4 mm
Mild Steel , Twin
Blades Pitch 45°
Nozzle Type
Nozzle Diameter
Nozzle Hole Diameter
Mould Type
Graphite
25.4 mm
10 mm
Stainless Steel
Mould Pretreatment
Sandpaper and coat with graphite spray
Stirrer Diameter
Stirrer Pretreament
75 mm
Coat with zirtex
Mould Diameter
Stirrer Clamping Position
40 mm
425 mm from blade
Stirring Position
Stirring Temperature
Bottom of melt
750 °C
Crucible Type
Crucible Size
Crucible Diameter
Crucible Hole Diameter
Stirrer Type
Reinforcement Addition and Stirring
Stirring Speed
Stirring Duration
500 rpm
3 min
Argon Supply
Before Stirring
5 l/min
During Stirring
5 l/min
Melt Disintegration and Deposition Parameters
Disintegrating Gas
Nozzle Diameter
Disintegrating Gas Flow
Rate
Pouring Temperature
Disintegrating Duration
2 nozzles
4 mm diameter
25 l/min
750 °C
8 sec
Initial Weight
Deposited Weight
(after casting)
1500.00g
Deposited Ingot Height
450mm
1450.00g
Deposited Yield %
96.67%
Disinte grating Gas Type
Argon
Disintegrating Gas Pressure
Total Flight Distance
Disintegrating Flight
Distance
150 bar
765 mm
500 mm
Process Percentage Yield
Remarks
Weather – Fair
Shrinkage cavity observed at top of ingot
Appendix
General Description
Experiment No.
MMC System
6
Al-Mg/Al2O3
17th July 2002
Unsuccessful
Date
Status
Raw Materials
Material Type
Weight
Weight Percentage
Form
Pre-treatment
Matrix
Al + Mg
577.86g Al + 8g Mg
72.17% Al + 1% Mg
Al Granules + Mg Turnings
-
Reinforcement
Al2O3
214.64g
26.83%
0.05µm particulates
Preheat at 500°C for 1 hour
Heating Temperatures
1530h
Initial Temp.
30 °C
Ending Time
1715h
Final Temp.
Time taken to reach
required temperature
750 °C
900
Temp. (oC)
Starting Time
600
300
0
0
1.75 hrs
60
120
180
Time (mins)
Equipment Parameters
Graphite
A12
105 mm
25.4 mm
Mild Steel , Twin
Blades Pitch 45°
Nozzle Type
Nozzle Diameter
Nozzle Hole Diameter
Mould Type
Graphite
25.4 mm
10 mm
Stainless Steel
Mould Pretreatment
Sandpaper and coat with graphite spray
Stirrer Diameter
Stirrer Pretreament
75 mm
Coat with zirtex
Mould Diameter
Stirrer Clamping Position
40 mm
425 mm from blade
Stirring Position
Stirring Temperature
Bottom of melt
750 °C
Crucible Type
Crucible Size
Crucible Diameter
Crucible Hole Diameter
Stirrer Type
Reinforcement Addition and Stirring
Stirring Speed
Stirring Duration
500 rpm
3 min
Argon Supply
Before Stirring
5 l/min
During Stirring
5 l/min
Melt Disintegration and Deposition Parameters
Disintegrating Gas
Nozzle Diameter
Disinte grating Gas Flow
Rate
Pouring Temperature
Disintegrating Duration
2 nozzles
4 mm diameter
25 l/min
750 °C
8 sec
Initial Weight
Deposited Weight
(after casting)
800.50g
Deposite d Ingot Height
-
-
Deposited Yield %
-
Disintegrating Gas Type
Argon
Disintegrating Gas Pressure
Total Flight Distance
Disintegrating Flight
Distance
150 bar
765 mm
500 mm
Process Percentage Yield
Remarks
Alumina does not wet. Large amounts of reinforcement material left in crucible.
Small quantity of pure aluminium flowed out.
Appendix
General Description
Experiment No.
MMC System
7
Al-Mg/Al2O3
24th July 2002
Unsuccessful
Date
Status
Raw Materials
Material Type
Weight
Weight Percentage
Form
Pre-treatment
Matrix
Al + Mg
787.19g Al + 16.065g Mg
77.85% Al + 2% Mg
Al Granules + Mg Turnings
-
Reinforcement
Al2O3
207.90g
20.15%
0.05µm particulates
Preheat at 500°C for 1 hour
Heating Temperatures
1405h
Initial Temp.
30 °C
Ending Time
1550h
Final Temp.
Time taken to reach
required temperature
750 °C
900
Temp. (oC)
Starting Time
600
300
0
0
1.75 hrs
60
120
180
Time (mins)
Equipment Parameters
Graphite
A12
105 mm
25.4 mm
Mild Steel , Twin
Blades Pitch 45°
Nozzle Type
Nozzle Diameter
Nozzle Hole Diameter
Mould Type
Graphite
25.4 mm
10 mm
Stainless Steel
Mould Pretreatment
Sandpaper and coat with graphite spray
Stirrer Diameter
Stirrer Pretreament
75 mm
Coat with zirtex
Mould Diameter
Stirrer Clamping Position
40 mm
425 mm from blade
Stirring Position
Stirring Temperature
Bottom of melt
750 °C
Crucible Type
Crucible Size
Crucible Diameter
Crucible Hole Diameter
Stirrer Type
Reinforcement Addition and Stirring
Stirring Speed
Stirring Duration
500 rpm
10 min
Argon Supply
Before Stirring
5 l/min
During Stirring
5 l/min
Melt Disintegration and Deposition Parameters
Disintegrating Gas
Nozzle Diameter
Disintegrating Gas Flow
Rate
Pouring Temperature
Disintegrating Duration
2 nozzles
4 mm diameter
25 l/min
750 °C
8 sec
Initial Weight
Deposited Weight
(after casting)
1011.16g
Deposited Ingot Height
-
-
Deposited Yield %
-
Disintegrating Gas Type
Argon
Disintegrating Gas Pressure
Total Flight Distance
Disintegrating Flight
Distance
150 bar
765 mm
500 mm
Process Percentage Yield
Remarks
Large amounts of powder left behind in crucible.
Small quantity of ingot cast.
Appendix
General Description
Experiment No.
MMC System
8
Al-Mg/Al2O3
26th July 2002
Unsuccessful
Date
Status
Raw Materials
Material Type
Weight
Weight Percentage
Form
Pre-treatment
Matrix
Al + Mg
952.56g Al + 19.44g Mg
84% Al + 2% Mg
Al Granules + Mg Turnings
-
Reinforcement
Al2O3
158.40g
14%
0.05µm particulates
Preheat at 500°C for 1hour
Heating Temperatures
Starting Time
1350h
Initial Temp.
30 °C
Ending Time
1650h
Final Temp.
Time taken to reach
required temperature
950 °C
Crucible Type
Crucible Size
Crucible Diameter
Crucible Hole Diameter
Graphite
A12
105 mm
25.4 mm
Mild Steel , Twin
Blades Pitch 45°
Nozzle Type
Nozzle Diameter
Nozzle Hole Diameter
Mould Type
Graphite
25.4 mm
10 mm
Stainless Steel
Mould Pretreatment
Sandpaper and coat with graphite spray
Stirrer Diameter
Stirrer Pretreament
75 mm
Coat with zirtex
Mould Diameter
Stirrer Clamping Position
40 mm
425 mm from blade
Stirring Position
Stirring Temperature
Bottom of melt
950 °C
Temp. (oC)
900
600
300
0
3 hrs
0
60
120
180
240
300
Time (mins)
Equipment Parameters
Stirrer Type
Reinforcement Addition and Stirring
Stirring Speed
Stirring Duration
500 rpm
10 min
Argon Supply
Before Stirring
5 l/min
During Stirring
5 l/min
Melt Disintegration and Deposition Parameters
Disintegrating Gas
Nozzle Diameter
Disintegrating Gas Flow
Rate
Pouring Temperature
Disintegrating Duration
2 nozzles
4 mm diameter
25 l/min
750 °C
8 sec
Initial Weight
Deposited Weight
(after casting)
1130.40g
Deposited Ingot Height
-
-
Deposited Yield %
-
Disintegrating Gas Type
Argon
Disintegrating Gas Pressure
Total Flight Distance
Disintegrating Flight
Distance
150 bar
765 mm
500 mm
Process Percentage Yield
Remarks
Stirrer blade corroded.
Large amount of powder retained in crucible. All aluminium melt flowed.
Appendix
General Description
Experiment No.
MMC System
9
Al-Mg/Al2O3
1st August 2002
Unsuccessful
Date
Status
Raw Materials
Material Type
Weight
Weight Percentage
Form
Pre-treatment
Matrix
Al + Mg
952.56g Al + 19.44g Mg
84% Al + 2% Mg
Al Granules + Mg Turnings
-
Reinforcement
Al2O3
158.40g
14%
0.05µm particulates
Preheat at 500°C for 1hour
Heating Temperatures
Starting Time
1600h
Initial Temp.
30 °C
Ending Time
1745h
Final Temp.
Time taken to reach
required temperature
750 °C
9 0 0
6 0 0
3 0 0
0
0
1.75 hrs
6 0
120
180
Time (mins)
Equipment Parameters
Graphite
A12
105 mm
25.4 mm
Mild Steel , Twin
Blades Pitch 45°
Nozzle Type
Nozzle Diameter
Nozzle Hole Diameter
Mould Type
Graphite
25.4 mm
10 mm
Stainless Steel
Mould Pretreatment
Sandpaper and coat with graphite sp ray
Stirrer Diameter
Stirrer Pretreament
75 mm
Coat with zirtex
Mould Diameter
Stirrer Clamping Position
40 mm
425 mm from blade
Stirring Position
Stirring Temperature
Bottom of melt
750 °C
Crucible Type
Crucible Size
Crucible Diameter
Crucible Hole Diameter
Stirrer Type
Reinforcement Addition and Stirring
Stirring Speed
Stirring Duration
500 rpm
5 min
Argon Supply
Before Stirring
5 l/min
During Stirring
5 l/min
Melt Disintegration and Deposition Parameters
Disintegrating Gas
Nozzle Diameter
Disintegrating Gas Flow
Rate
Pouring Temperature
Disintegrating Duration
2 nozzles
4 mm diameter
25 l/min
750 °C
8 sec
Initial Weight
Deposited Weight
(after casting)
1130.40g
Deposited Ingot Height
-
-
Deposited Yield %
-
Disintegrating Gas Type
Argon
Disintegrating Gas Pressure
Total Flight Distance
Disintegrating Flight
Distance
150 bar
765 mm
500 mm
Process Percentage Yield
Remarks
Large amount of powder retained in crucible.
All aluminium melt flowed.
Appendix
General Description
Experiment No.
MMC System
10
Al-Mg/Al2O3
7th August 2002
Success
Date
Status
Raw Materials
Material Type
Weight
Weight Percentage
Form
Pre-treatment
Matrix
Al + Mg
983.89g Al + 20.08g Mg
88% Al + 2% Mg
Al Granules + Mg Turnings
-
Reinforcement
Al2O3
111.51g
10%
0.05µm particulates
Preheat at 500°C for 1hour
Heating Temperatures
Starting Time
1625h
Initial Temp.
30 °C
Ending Time
1810h
Final Temp.
Time taken to reach
required temperature
750 °C
9 0 0
6 0 0
3 0 0
0
0
1.75 hrs
6 0
120
180
Time (mins)
Equipment Parameters
Graphite
A12
105 mm
25.4 mm
Mild Steel , Twin
Blades Pitch 45°
Nozzle Type
Nozzle Diameter
Nozzle Hole Diameter
Mould Type
Graphite
25.4 mm
10 mm
Stainless Steel
Mould Pretreatment
Sandpaper and coat with graphite spray
Stirrer Diameter
Stirrer Pretreament
75 mm
Coat with zirtex
Mould Diameter
Stirrer Clamping Position
40 mm
425 mm from blade
Stirring Position
Stirring Temperature
Bottom of melt
750 °C
Crucible Type
Crucible Size
Crucible Diameter
Crucible Hole Diameter
Stirrer Type
Reinforcement Addition and Stirring
Stirring Speed
Stirring Duration
500 rpm
10 min
Argon Supply
Before Stirring
5 l/min
During Stirring
5 l/min
Melt Disintegration and Deposition Parameters
Disintegrating Gas
Nozzle Diameter
Disintegrating Gas Flow
Rate
Pouring Temperature
Disintegrating Duration
2 nozzles
4 mm diameter
25 l/min
750 °C
8 sec
Initial Weight
Deposited Weight
(after casting)
1115.48g
Deposited Ingot Height
200mm
653.73g
Deposited Yield %
58.6%
Disintegrating Gas Type
Argon
Disintegrating Gas Pressure
Total Flight Distance
Disintegrating Flight
Distance
150 bar
765 mm
500 mm
Process Percentage Yield
Remarks
Weather – Fair
Shrinkage cavity observed at top of ingot.
Appendix
General Description
Experiment No.
MMC System
11
Al-Mg/Al2O3
15th August 2002
Success
Date
Status
Raw Materials
Material Type
Weight
Weight Percentage
Form
Pre-treatment
Matrix
Al + Mg
963.81g Al + 40.16g Mg
86% Al + 4% Mg
Al Granules + Mg Turnings
-
Reinforcement
Al2O3
111.51g
10%
0.05µm particulates
Preheat at 500°C for 1 hour
Heating Temperatures
1410h
Initial Temp.
30 °C
Ending Time
1555h
Final Temp.
Time taken to reach
required temperature
750 °C
900
Temp. (oC)
Starting Time
600
300
0
0
1.75 hrs
60
120
180
Time (mins)
Equipment Parameters
Graphite
A12
105 mm
25.4 mm
Mild Steel , Twin
Blades Pitch 45°
Nozzle Type
Nozzle Diameter
Nozzle Hole Diameter
Mould Type
Graphite
25.4 mm
10 mm
Stainless Steel
Mould Pretreatment
Sandpaper and coat with graphite spray
Stirrer Diameter
Stirrer Pretreament
75 mm
Coat with zirtex
Mould Diameter
Stirrer Clamping Position
40 mm
425 mm from blade
Stirring Position
Stirring Temperature
Bottom of melt
750 °C
Crucible Type
Crucible Size
Crucible Diameter
Crucible Hole Diameter
Stirrer Type
Reinforcement Addition and Stirring
Stirring Speed
Stirring Duration
500 rpm
10 min
Argon Supply
Before Stirring
5 l/min
During Stirring
5 l/min
Melt Disintegration and Deposition Parameters
Disintegrating Gas
Nozzle Diameter
Disintegrating Gas Flow
Pouring Rate
Temperature
Disintegrating Duration
2 nozzles
4 mm diameter
25 l/min
750 °C
8 sec
Initial Weight
Deposited Weight
(after casting)
1115.50g
Deposited Ingot Height
220mm
746.80g
Deposited Yield %
66.9%
Disintegrating Gas Type
Argon
Disintegrating Gas Pressure
Total Flight Distance
Disintegrating Flight
Distance
150 bar
765 mm
500 mm
Process Percentage Yield
Remarks
Weather – Fair
Shrinkage cavity observed at top of ingot
Appendix
General Description
12
Al-Mg/Al2O3
Experiment No.
MMC System
26th September 2002
Unsuccessful
Date
Status
Raw Materials
Material Type
Weight
Weight Percentage
Form
Pre-treatment
Matrix
Al + Mg
953.77g Al + 50.2g Mg
85% Al + 5% Mg
Al Granules + Mg Turnings
-
Reinforcement
Al2O3
111.51g
10%
0.05µm particulates
Preheat at 500°C for 1 hour
Heating Temperatures
1435h
Initial Temp.
30 °C
Ending Time
1620h
Final Temp.
Time taken to reach
required temperature
750 °C
900
Temp. (oC)
Starting Time
600
300
0
0
1.75 hrs
60
120
180
Time (mins)
Equipment Parameters
Graphite
A12
105 mm
25.4 mm
Mild Steel , Twin
Blades Pitch 45°
Nozzle Type
Nozzle Diameter
Nozzle Hole Diameter
Mould Type
Graphite
25.4 mm
10 mm
Stainless Steel
Mould Pretreatment
Sandpaper and coat with graphite spray
Stirrer Diameter
Stirrer Pretreament
75 mm
Coat with zirtex
Mould Diameter
Stirrer Clamping Position
40 mm
425 mm from blade
Stirring Position
Stirring Temperature
Bottom of melt
750 °C
Crucible Type
Crucible Size
Crucible Diameter
Crucible Hole Diameter
Stirrer Type
Reinforcement Addition and Stirring
Stirring Speed
Stirring Duration
500 rpm
10 min
Argon Supply
Before Stirring
5 l/min
During Stirring
5 l/min
Melt Disintegration and Deposition Parameters
Disintegrating Gas
Nozzle Diameter
Disintegrating Gas Flow
Rate
Pouring Temperature
Disintegrating Duration
2 nozzles
4 mm diameter
25 l/min
750 °C
8 sec
Initial Weight
Deposited Weight
(after casting)
1115.50g
Deposited Ingot Height
-
-
Deposited Yield %
-
Disintegrating Gas Type
Argon
Disintegrating Gas Pressure
Total Flight Distance
Disintegrating Flight
Distance
150 bar
765 mm
500 mm
Process Percentage Yield
Remarks
Stirrer badly corroded.
Appendix
General Description
Experiment No.
MMC System
13
Al-Mg/Al2O3
11th October 2002
Success
Date
Status
Raw Materials
Material Type
Weight
Weight Percentage
Form
Pre-treatment
Matrix
Al + Mg
953.77g Al + 50.2g Mg
85% Al + 5% Mg
Al Granules + Mg Turnings
-
Reinforcement
Al2O3
111.51g
10%
0.05µm particulates
Preheat at 500°C for 1 hour
Heating Temperatures
1040h
Initial Temp.
30 °C
Ending Time
1225h
Final Temp.
Time taken to reach
required temperature
750 °C
900
Temp. (oC)
Starting Time
600
300
0
0
1.75 hrs
60
120
180
Time (mins)
Equipment Parameters
Graphite
A12
105 mm
25.4 mm
Mild Steel , Twin
Blades Pitch 45°
Nozzle Type
Nozzle Diameter
Nozzle Hole Diameter
Mould Type
Graphite
25.4 mm
10 mm
Stainless Steel
Mould Pretreatment
Sandpaper and coat with graphite spray
Stirrer Diameter
Stirrer Pretreament
75 mm
Coat with zirtex
Mould Diameter
Stirrer Clamping Position
40 mm
425 mm from blade
Stirring Position
Stirring Temperature
Bottom of melt
750 °C
Crucible Type
Crucible Size
Crucible Diameter
Crucible Hole Diameter
Stirrer Type
Reinforcement Addition and Stirring
Stirring Speed
Stirring Duration
500 rpm
10 min
Argon Supply
Before Stirring
5 l/min
During Stirring
5 l/min
Melt Disintegration and Deposition Parameters
Disintegrating Gas
Nozzle Diameter
Disintegrating Gas Flow
Rate
Pouring Temperature
Disintegrating Duration
2 nozzles
4 mm diameter
25 l/min
750 °C
8 sec
Initial Weight
Deposited Weight
(after casting)
1115.50g
Deposited Ingot Height
210mm
730.50g
Deposited Yield %
65.5%
Disintegrating Gas Type
Argon
Disintegrating Gas Pressure
Total Flight Distance
Disintegrating Flight
Distance
150 bar
765 mm
500 mm
Process Percentage Yield
Remarks
Weather – Fair
Shrinkage cavity observed at top of ingot
Appendix
General Description
14
Al-Mg
Experiment No.
MMC System
7th January 2003
Success
Date
Status
Raw Materials
Material Type
Weight
Weight Percentage
Form
Pre-treatment
Matrix
Al + Mg
1162.76g Al + 52.25g Mg
95.7% Al + 4.3% Mg
Al Granules + Mg Turnings
-
Reinforcement
-
Heating Temperatures
Starting Time
1410h
Initial Temp.
30 °C
Ending Time
1610h
Final Temp.
Time taken to reach
required temperature
750 °C
Crucible Type
Crucible Size
Crucible Diameter
Crucible Hole Diameter
Graphite
A12
105 mm
25.4 mm
Mild Steel , Twin
Blades Pitch 45°
Nozzle Type
Nozzle Diameter
Nozzle Hole Diameter
Mould Type
Graphite
25.4 mm
10 mm
Stainless Steel
Mould Pretreatment
Sandpaper and coat with graphite spray
Stirrer Diameter
Stirrer Pretreament
75 mm
Coat with zirtex
Mould Diameter
Stirrer Clamping Position
40 mm
425 mm from blade
Stirring Position
Stirring Temperature
Bottom of melt
750 °C
Temp. (oC)
900
600
300
0
2 hrs
0
60
120
180
Time (mins)
Equipment Parameters
Stirrer Type
Reinforcement Addition and Stirring
Stirring Speed
Stirring Duration
500 rpm
10 min
Argon Supply
Before Stirring
5 l/min
During Stirring
5 l/min
Melt Disintegration and Deposition Parameters
Disintegrating Gas
Nozzle Diameter
Disintegrating Gas Flow
Rate
Pouring Temperature
Disintegrating Duration
2 nozzles
4 mm diameter
25 l/min
750 °C
8 sec
Initial Weight
Deposited Weight
(after casting)
1215.00g
Deposited Ingot Height
340mm
1075.00g
Deposited Yield %
88.5%
Disintegrating Gas Type
Argon
Disinte grating Gas Pressure
Total Flight Distance
Disintegrating Flight
Distance
150 bar
765 mm
500 mm
Process Percentage Yield
Remarks
Weather – Fair
Shrinkage cavity observed at top of ingot
Appendix
General Description
Experiment No.
MMC System
15
Al-Mg/Al2O3
9th January 2003
Success
Date
Status
Raw Materials
Material Type
Weight
Weight Percentage
Form
Pre-treatment
Matrix
Al + Mg
1072.99g Al + 56.47g Mg
85% Al + 5% Mg
Al Granules + Mg Turnings
-
Reinforcement
Al2O3
125.45g
10%
0.3µm particulates
Preheat at 500°C for 1 hour
Heating Temperatures
1430h
Initial Temp.
30 °C
Ending Time
1615h
Final Temp.
Time taken to reach
required temperature
750 °C
900
Temp. (oC)
Starting Time
600
300
0
0
1.75 hrs
60
120
180
Time (mins)
Equipment Parameters
Graphite
A12
105 mm
25.4 mm
Mild Steel , Twin
Blades Pitch 45°
Nozzle Type
Nozzle Diameter
Nozzle Hole Diameter
Mould Type
Graphite
25.4 mm
10 mm
Stainless Steel
Mould Pretreatment
Sandpaper and coat with graphite spray
Stirrer Diameter
Stirrer Pretreament
75 mm
Coat with zirtex
Mould Diameter
Stirrer Clamping Position
40 mm
425 mm from blade
Stirring Position
Stirring Temperature
Bottom of melt
750 °C
Crucible Type
Crucible Size
Crucible Diameter
Crucible Hole Diameter
Stirrer Type
Reinforcement Addition and Stirring
Stirring Speed
Stirring Duration
500 rpm
10 min
Argon Supply
Before Stirring
5 l/min
During Stirring
5 l/min
Melt Disintegration and Deposition Parameters
Disintegrating Gas
Nozzle Diameter
Disintegrating Gas Flow
Pouring Rate
Temperature
Disintegrating Duration
2 nozzles
4 mm diameter
25 l/min
750 °C
8 sec
Initial Weight
Deposited Weight
(after casting)
1254.91g
Deposited Ingot Height
245mm
802.00g
Deposite d Yield %
63.9%
Disintegrating Gas Type
Argon
Disintegrating Gas Pressure
Total Flight Distance
Disintegrating Flight
Distance
150 bar
765 mm
500 mm
Process Percentage Yield
Remarks
Weather – Fair
Shrinkage cavity observed at top of ingot
Appendix
General Description
Experiment No.
MMC System
16
Al-Mg/Al2O3
14th January 2003
Success
Date
Status
Raw Materials
Material Type
Weight
Weight Percentage
Form
Pre-treatment
Matrix
Al + Mg
1072.99g Al + 56.47g Mg
85% Al + 5% Mg
Al Granules + Mg Turnings
-
Reinforcement
Al2O3
125.45g
10%
1µm particulates
Preheat at 500°C for 1 hour
Heating Temperatures
1335h
Initial Temp.
30 °C
Ending Time
1520h
Final Temp.
Time taken to reach
required temperature
750 °C
900
Temp. (oC)
Starting Time
600
300
0
0
1.75 hrs
60
120
180
Time (mins)
Equipment Parameters
Graphite
A12
105 mm
25.4 mm
Mild Steel , Twin
Blades Pitch 45°
Nozzle Type
Nozzle Diameter
Nozzle Hole Diameter
Mould Type
Graphite
25.4 mm
10 mm
Stainless Steel
Mould Pretreatment
Sandpaper and coat with graphite spray
Stirrer Diameter
Stirrer Pretreament
75 mm
Coat with zirtex
Mould Diameter
Stirrer Clamping Position
40 mm
425 mm from blade
Stirring Position
Stirring Temperature
Bottom of melt
750 °C
Crucible Type
Crucible Size
Crucible Diameter
Crucible Hole Diameter
Stirrer Type
Reinforcement Addition and Stirring
Stirring Speed
Stirring Duration
500 rpm
10 min
Argon Supply
Before Stirring
5 l/min
During Stirring
5 l/min
Melt Disintegration and Deposition Parameters
Disintegrating Gas
Nozzle Diameter
Disintegrating Gas Flow
Rate
Pouring Temperature
Disintegrating Duration
2 nozzles
4 mm diameter
25 l/min
750 °C
8 sec
Initial Weight
Deposited Weight
(after casting)
1254.91g
Deposited Ingot Height
230mm
725.00g
Deposited Yield %
57.8%
Disintegrating Gas Type
Argon
Disintegrating Gas Pressure
Total Flight Distance
Disintegrating Flight
Distance
150 bar
765 mm
500 mm
Process Percentage Yield
Remarks
Weather – Fair
Shrinkage cavity observed at top of ingot
Appendix
General Description
Experiment No.
MMC System
17
Al-Mg/Al2O3
16th January 2003
Success
Date
Status
Raw Materials
Material Type
Weight
Weight Percentage
Form
Pre-treatment
Matrix
Al + Mg
1072.99g Al + 56.47g Mg
85% Al + 5% Mg
Al Granules + Mg Turnings
-
Reinforcement
Al2O3
125.45g
10%
10µm particulates
Preheat at 500°C for 1 hour
Heating Temperatures
1440h
Initial Temp.
30 °C
Ending Time
1625h
Final Temp.
Time taken to reach
required temperature
750 °C
900
Temp. (oC)
Starting Time
600
300
0
0
1.75 hrs
60
120
180
Time (mins)
Equipment Parameters
Graphite
A12
105 mm
25.4 mm
Mild Steel , Twin
Blades Pitch 45°
Nozzle Type
Nozzle Diameter
Nozzle Hole Diameter
Mould Type
Graphite
25.4 mm
10 mm
Stainless Steel
Mould Pretreatment
Sandpaper and coat with graphite spray
Stirrer Diameter
Stirrer Pretreament
75 mm
Coat with zirtex
Mould Diameter
Stirrer Clamping Position
40 mm
425 mm from blade
Stirring Position
Stirring Temperature
Bottom of melt
750 °C
Crucible Type
Crucible Size
Crucible Diameter
Crucible Hole Diameter
Stirrer Type
Reinforcement Addition and Stirring
Stirring Speed
Stirring Duration
500 rpm
10 min
Argon Supply
Before Stirring
5 l/min
During Stirring
5 l/min
Melt Disintegration and Deposition Parameters
Disintegrating Gas
Nozzle Diameter
Disintegrating Gas Flow
Rate
Pouring Temperature
Disintegrating Durati on
2 nozzles
4 mm diameter
25 l/min
750 °C
8 sec
Initial Weight
Deposited Weight
(after casting)
1254.91g
Deposited Ingot Height
260mm
893.00g
Deposited Yield %
71.2%
Disintegrating Gas Type
Argon
Disintegrating Gas Pressure
Total Flight Distance
Disintegrating Flight
Distance
150 bar
765 mm
500 mm
Process Percentage Yield
Remarks
Weather – Fair
Shrinkage cavity observed at top of ingot
Appendix
General Description
18
Al-Mg
Experiment No.
MMC System
22nd January 2003
Success
Date
Status
Raw Materials
Material Type
Weight
Weight Percentage
Form
Pre-treatment
Matrix
Al + Mg
1162.76g Al + 52.25g Mg
95.7% Al + 4.3% Mg
Al Granules + Mg Turnings
-
Reinforcement
-
Heating Temperatures
1420h
Initial Temp.
30 °C
Ending Time
1610h
Final Temp.
Time taken to reach
required temperature
750 °C
900
Temp. (oC)
Starting Time
600
300
0
0
1.75 hrs
60
120
180
Time (mins)
Equipment Parameters
Graphite
A12
105 mm
25.4 mm
Mild Steel , Twin
Blades Pitch 45°
Nozzle Type
Nozzle Diameter
Nozzle Hole Diameter
Mould Type
Graphite
25.4 mm
10 mm
Stainless Steel
Mould Pretreatment
Sandpaper and coat with graphite spray
Stirrer Diameter
Stirrer Pretreament
75 mm
Coat with zirtex
Mould Diameter
Stirrer Clamping Position
40 mm
425 mm from blade
Stirring Position
Stirring Temperature
Bottom of melt
750 °C
Crucible Type
Crucible Size
Crucible Diameter
Crucible Hole Diameter
Stirrer Type
Reinforcement Addition and Stirring
Stirring Speed
Stirring Duration
500 rpm
10 min
Argon Supply
Before Stirring
5 l/min
During Stirring
5 l/min
Melt Disintegration and Deposition Parameters
Disintegrating Gas
Nozzle Diameter
Disintegrating Gas Flow
Rate
Pouring Temperature
Disintegrating Duration
2 nozzles
4 mm diameter
25 l/min
750 °C
8 sec
Initial Weight
Deposited Weight
(after casting)
1215.00g
Deposited Ingot Height
320mm
1050.00g
Deposited Yield %
86.4%
Disintegrating Gas Type
Argon
Disintegrating Gas Pressure
Total Flight Distance
Disintegrating Flight
Distance
150 bar
765 mm
500 mm
Process Percentage Yield
Remarks
Weather – Fair
Shrinkage cavity observed at top of ingot
Appendix
Appendix B: Experimental setup and results for density measurement
Specimen Holder
Specimen Hanger
Glass Beaker
Specimen
Distilled Water
Supporting Stand
Electronic Balance
Experimental density is calculated using the equation,
ρ=
ρ l Wa − ρ aWl
Wa − Wl
where subscripts a and l refer to air and liquid respectively.
Porosity of pure aluminium is calculated using the equation,
Porosity =
ρth − ρ e
ρ th − ρa
Percentage porosity = Porosity × 100
where ρth = Theoretical density
ρe = Experimental density
ρa = Density of air
Appendix
Table B-1:
Density and porosity of pure aluminium materials in Phases I & II.
Al25 (8mm)
Wair (g)
Wwater (g)
Density (gcm-3)
Mean (gcm-3)
Std. Dev.
Vol. % Porosity
Al85 (8mm)
Wair (g)
Wwater (g)
Density (gcm-3)
Mean (gcm-3)
Std. Dev.
Vol. % Porosity
Al150 (8mm)
Wair (g)
Wwater (g)
Density (gcm-3)
Mean (gcm-3)
Std. Dev.
Vol. % Porosity
Al250 (8mm)
Wair (g)
Wwater (g)
Density (gcm-3)
Mean (gcm-3)
Std. Dev.
Vol. % Porosity
1
1.280
0.806
2.700
1
1.240
0.781
2.699
1
1.240
0.780
2.695
1
1.233
0.776
2.698
Specimen
2
1.234
0.777
2.698
2.696
0.005
0.142
Specimen
2
1.244
0.783
2.699
2.698
0.002
0.083
Specimen
2
1.233
0.777
2.700
2.698
0.002
0.072
Specimen
2
1.233
0.776
2.698
2.699
0.001
0.052
3
1.309
0.823
2.691
3
1.244
0.783
2.695
3
1.246
0.785
2.699
3
1.230
0.774
2.700
Appendix
Table B-2:
Density and porosity of pure aluminium materials in Phases I & II.
Al350 (8mm)
Wair (g)
Wwater (g)
Density (gcm-3)
Mean (gcm-3)
Std. Dev.
Vol. % Porosity
1
1.218
0.765
2.690
Specimen
2
1.220
0.768
2.700
2.695
0.005
0.167
3
1.218
0.767
2.697
Wair (g)
1
0.920
Specimen
2
0.927
3
0.928
Wwater (g)
0.579
0.583
0.584
2.698
2.692
2.698
Al-7 (7mm)
Density (gcm-3)
-3
Mean (gcm )
Std. Dev.
Vol. % Porosity
Al-10 (10mm)
Wair (g)
Wwater (g)
-3
Density (gcm )
Mean (gcm-3)
Std. Dev.
Vol. % Porosity
2.696
0.003
0.135
1
1.465
Specimen
2
1.630
3
1.572
0.921
1.027
0.990
2.691
2.700
2.700
2.697
0.005
0.112
Appendix
Table B-3:
Density and porosity of composite materials in Phase III.
Al-1.6Mg/Al2O3 (0.05µm)
Wair (g)
Wwater (g)
Density (gcm-3)
Mean (gcm-3)
Std. Dev.
Vol. % Porosity
Al-2.9Mg/Al2O3 (0.05µm)
Wair (g)
Wwater (g)
Density (gcm-3)
Mean (gcm-3)
Std. Dev.
Vol. % Porosity
Al-3.4Mg/Al2O3 (0.05µm)
Wair (g)
Wwater (g)
Density (gcm-3)
Mean (gcm-3)
Std. Dev.
Vol. % Porosity
a
1
1.065
0.670
2.693
1
1.061
0.664
2.671
1
1.065
0.666
2.667
Specimen
2
1.180
0.741
2.687
2.696
0.011
0.075a
Specimen
2
1.119
0.701
2.678
2.669
0.009
0.039a
Specimen
2
1.096
0.685
2.668
2.662
0.009
0.114a
3
1.204
0.760
2.708
3
1.112
0.694
2.660
3
1.119
0.697
2.651
Result of cumulative image analysis conducted on 10 representative SEM micrographs.
Appendix
Table B-4:
Density and porosity of composite materials in Phase IV.
Al-Mg
Wair (g)
Wwater (g)
Density (gcm-3)
Mean (gcm-3)
Std. Dev.
Vol. % Porosity
Al-Mg-0.3µm Al2O3
Wair (g)
Wwater (g)
Density (gcm-3)
Mean (gcm-3)
Std. Dev.
Vol. % Porosity
Al-Mg-1µm Al2 O3
Wair (g)
Wwater (g)
Density (gcm-3)
Mean (gcm-3)
Std. Dev.
Vol. % Porosity
1
1.063
0.661
2.645
1
1.063
0.662
2.649
Specimen
2
1.061
0.659
2.636
2.646
0.010
0.041a
Specimen
2
1.023
0.636
2.641
2.647
0.005
0.021a
3
1.061
0.660
2.641
3
1.062
0.663
2.657
3
1.053
0.656
2.651
Wair (g)
1
1.064
Specimen
2
1.066
3
1.041
Wwater (g)
0.664
0.665
0.649
Density (gcm-3)
Mean (gcm-3)
Std. Dev.
Vol. % Porosity
2.659
2.656
2.657
0.002
1.033a
2.657
Al-Mg-10µm Al2 O3
a
1
1.061
0.659
2.636
Specimen
2
1.060
0.660
2.645
2.641
0.005
0.056a
Result of cumulative image analysis conducted on 10 representative SEM micrographs.
Appendix
Appendix C: XRD Results
Table C-1: XRD results of Al-1.6Mg/Al2 O3 .
Standard d-Spacing
(Å)
Al
Mg
2.605 *
2.4519 *
2.338 *
2.024 *
1.431
1.3027
1.221 *
1.169
5
3
3
2
Experimental
Intensity
d-Spacing (Å)
(counts)
2.605
498
2.4519
220
2.338
86890
2.024
1852
1.431
68
1.3027
50
1.221
306
1.169
7564
No. of peaks matched
No. of strong peaks matched
2000
1800
1600
Al
1400
Intensity (cps)
Mg
1200
1000
800
600
400
200
0
30
40
50
60
70
2 Theta (°)
Figure C-1: XRD spectrum of Al-1.6Mg/Al2 O3 .
80
90
Appendix
Table C-2: XRD results of Al-2.9Mg/Al2 O3 .
Experimental
Intensity
d-Spacing (Å)
(counts)
2.605
454
2.4519
274
2.338
92152
2.24
112
2.024
3056
1.431
54
1.3027
58
1.221
416
1.169
7370
No. of peaks matched
No. of strong peaks matched
Standard d-Spacing (Å)
Al
Mg
2.605 *
2.4519 *
Al12Mg17
2.338 *
2.24 *
2.024 *
1.431
1.3027
1.221 *
1.169
5
3
3
2
1
1
2000
1800
Al
Mg
1600
Al12Mg 17
Intensity (cps)
1400
1200
1000
800
600
400
200
0
30
40
50
60
70
2 Theta (°)
Figure C-2: XRD spectrum of Al-2.9Mg/Al2 O3 .
80
90
Appendix
Table C-3: XRD results of Al-3.4Mg/Al2 O3 .
Experimental
Intensity
d-Spacing (Å)
(counts)
2.605
568
2.4519
306
2.338
107398
2.24
126
2.024
7392
1.431
70
1.3027
72
1.221
292
1.169
9766
No. of peaks matched
No. of strong peaks matched
Standard d-Spacing (Å)
Al
Mg
2.605 *
2.4519 *
Al12Mg17
2.338 *
2.24 *
2.024 *
1.431
1.3027
1.221 *
1.169
5
3
3
2
1
1
2000
1800
Al
1600
Mg
Al12Mg17
Intensity (cps)
1400
1200
1000
800
600
400
200
0
30
40
50
60
70
2 Theta (°)
Figure C-3: XRD spectrum of Al-3.4Mg/Al2 O3 .
80
90
Appendix
Table C-4: XRD results of Al-Mg.
Experimental
Intensity
d-Spacing (Å)
(counts)
2.605
606
2.4519
290
2.338
120986
2.24
176
2.024
18730
1.431
48
1.3027
80
1.221
376
1.169
10308
No. of peaks matched
No. of strong peaks matched
Standard d-Spacing (Å)
Al
Mg
2.605 *
2.4519 *
Al12Mg17
2.338 *
2.24 *
2.024 *
1.431
1.3027
1.221 *
1.169
5
3
3
2
1
1
2000
Al
1800
Mg
1600
Al12Mg17
Intensity (counts)
1400
1200
1000
800
600
400
200
0
30
40
50
60
70
2 Theta (°)
Figure C-4: XRD spectrum of Al-Mg.
80
90
Appendix
Table C-5: XRD results of Al-Mg-0.3µm Al2 O3 .
Experimental
Intensity
d-Spacing (Å)
(counts)
2.605
520
2.4519
292
2.338
104058
2.24
152
2.024
12256
1.431
48
1.3027
66
1.221
320
1.169
8456
No. of peaks matched
No. of strong peaks matched
Standard d-Spacing (Å)
Al
Mg
2.605 *
2.4519 *
Al12Mg17
2.338 *
2.24 *
2.024 *
1.431
1.3027
1.221 *
1.169
5
3
3
2
1
1
2000
Al
1800
Mg
Al12Mg 17
1600
Intensity (cps)
1400
1200
1000
800
600
400
200
0
30
40
50
60
70
2 Theta (°)
Figure C-5: XRD spectrum of Al-Mg-0.3µm Al2 O3 .
80
90
Appendix
Table C-6: XRD results of Al-Mg-1µm Al2 O3 .
Experimental
Intensity
d-Spacing (Å)
(counts)
2.605
578
2.4519
294
2.338
114006
2.24
156
2.024
14296
1.431
70
1.3027
78
1.221
488
1.169
10454
No. of peaks matched
No. of strong peaks matched
Standard d-Spacing (Å)
Al
Mg
2.605 *
2.4519 *
Al12Mg17
2.338 *
2.24 *
2.024 *
1.431
1.3027
1.221 *
1.169
5
3
3
2
1
1
2000
1800
Al
Mg
1600
Al12Mg17
Intensity (cps)
1400
1200
1000
800
600
400
200
0
30
40
50
60
70
2 Theta (°)
Figure C-6: XRD spectrum of Al-Mg-1µm Al2 O3 .
80
90
Appendix
Table C-7: XRD results of Al-Mg-10µm Al2 O3 .
Experimental
Intensity
d-Spacing (Å)
(counts)
2.605
256
2.4519
164
2.338
18040
2.086
56
2.024
1266
1.431
92
1.3739
44
1.3027
32
1.221
350
1.169
1530
No. of peaks matched
No. of strong peaks matched
Standard d-Spacing (Å)
Al
Mg
2.605 *
2.4519 *
Al2O3
2.338 *
2.086 *
2.024 *
1.431
1.3739
1.3027
1.221 *
1.169
5
3
3
2
2
1
2000
1800
Al
Mg
1600
Al2O3
Intensity (cps)
1400
1200
1000
800
600
400
200
0
30
40
50
60
70
2 Theta (°)
Figure C-7: XRD spectrum of Al-Mg-10µm Al2 O3 .
80
90
Appendix
Appendix D: Micro -hardness measurements
Table D-1: Micro-hardness values for Phase I & II
Specimen
Diameter (mm)
1
2
3
4
5
6
7
8
9
10
Mean
Std. Dev.
Extrusion
Load (Ton)
Extrusion
Ratio
Al25
8
49.4
45.1
45.3
49.2
51.3
47.4
49.4
49.9
49.4
49.6
48.6
2.0
Al85
8
45.2
44.2
45.6
48.0
47.5
48.9
46.4
45.6
46.6
47.7
46.6
1.5
Al150
8
41.4
45.9
44.2
45.7
46.6
47.8
45.5
45.1
46.1
47.6
45.6
1.8
Al250
8
37.2
41.6
42.8
41.6
42.6
41.7
41.4
41.7
41.7
41.0
41.3
1.5
Al350
8
35.7
36.0
34.0
35.7
36.7
35.3
36.3
37.0
38.6
35.2
36.1
1.2
Al-7
7
52.3
53.8
52.3
54.3
51.3
52.8
53.6
52.6
54.2
54.4
53.2
1.1
Al-10
10
46.1
45.1
46.8
43.6
44.2
47.13
44.93
46.23
46.53
43.93
45.5
1.3
65
70
60
50
50
70
80
20.25:1
20.25:1
20.25:1
20.25:1
20.25:1
26.45:1
12.96:1
Table D-2: Micro-hardness values for Phase III
Specimen
Al-1.6Mg/Al2O3
Al-2.9Mg/Al2O3
Al-3.4Mg/Al2O3
Diameter (mm)
1
2
3
4
5
6
7
8
9
10
Mean
Std. Dev.
Extrusion
Load (Ton)
Extrusion
Ratio
8
65.2
68.8
68.0
62.5
67.3
63.2
63.2
64.5
69.2
68.4
66.0
2.6
8
74.8
79.2
74.4
75.2
75.2
79.2
75.6
79.7
77.4
79.2
77.0
2.3
8
75.6
78.8
80.6
80.6
77.0
80.6
78.8
77.4
76.5
77.8
78.4
1.8
100
120
130
20.25:1
20.25:1
20.25:1
Appendix
Table D-3: Micro-hardness values for Phase IV
Specimen
Al-Mg
Al-Mg-0.05µm
Al2O3
Al-Mg-0.3µm
Al2O3
Al-Mg-1µm
Al2O3
Al-Mg-10µm
Al2O3
Diameter (mm)
1
2
3
4
5
6
7
8
9
10
Mean
Std. Dev.
Extrusion
Load (Ton)
Extrusion
Ratio
8
66.6
69.9
65.5
73.1
71.5
66.2
66.6
64.8
66.2
69.9
68.0
2.8
8
75.6
78.8
80.6
80.6
77.0
80.6
78.8
77.4
76.5
77.8
78.4
1.8
8
69.5
68.4
74.8
77.8
77.0
72.3
77.0
73.9
77.0
73.5
74.1
3.1
8
75.6
73.5
69.9
73.9
73.5
73.1
72.7
71.9
72.7
73.1
73.0
1.5
9
63.2
79.2
70.7
72.3
77.0
69.9
76.1
68.8
75.6
72.3
71.2
4.2
100
130
120
120
110
20.25:1
20.25:1
20.25:1
20.25:1
20.25:1
Appendix
Appendix E: Macro-hardness me asurements
Table E-1: Macro- hardness values for Phase I & II
Specimen
Diameter (mm)
1
2
3
4
5
6
7
8
9
10
Mean
Std. Dev.
Extrusion
Load (Ton)
Extrusion
Ratio
Al25
8
55.6
58.4
57.8
58.8
58.0
57.3
59.0
58.7
57.9
58.0
58.0
1.0
Al85
8
53.3
57.5
57.5
57.8
57.3
55.9
57.6
58.6
58.2
57.4
57.1
1.5
Al150
8
56.2
56.0
56.7
56.3
56.8
55.0
55.4
56.7
57.0
55.0
56.1
0.7
Al250
8
49.9
49.5
52.2
52.6
50.1
50.5
52.3
52.7
49.2
51.0
51.0
1.3
Al350
8
38.0
36.1
35.7
36.3
37.1
35.0
36.8
36.8
35.9
34.3
36.2
1.1
Al-7
7
58.1
58.2
58.4
58.8
58.1
57.8
57.7
57.6
57.5
57.7
58.0
0.4
Al-10
10
55.6
55.2
56.5
56.3
55.6
55.6
56.5
55.5
55.6
56.1
55.9
0.5
65
70
60
50
50
70
80
20.25:1
20.25:1
20.25:1
20.25:1
20.25:1
26.45:1
12.96:1
Table E-2: Macro- hardness values for Phase III
Specimen
Al-1.6Mg/Al2O3
Al-2.9Mg/Al2O3
Al-3.4Mg/Al2O3
Diameter (mm)
1
2
3
4
5
6
7
8
9
10
Mean
Std. Dev.
Extrusion
Load (Ton)
Extrusion
Ratio
8
68.0
66.0
66.6
67.7
64.5
67.0
68.5
68.2
68.3
68.3
67.3
1.3
8
71.7
71.5
72.7
72.3
72.0
71.2
71.3
70.6
71.2
72.1
71.7
0.6
8
74.4
75.1
73.1
75.1
73.6
73.3
73.0
71.9
70.9
71.1
73.2
1.5
100
120
130
20.25:1
20.25:1
20.25:1
Appendix
Table E-3: Macro- hardness values for Phase IV
Specimen
Diameter
(mm)
1
2
3
4
5
6
7
8
9
10
Mean
Std. Dev.
Extrusion
Load (Ton)
Extrusion
Ratio
Al-Mg
Al-Mg-0.05µm
Al2O3
Al-Mg-0.3µm
Al2O3
Al-Mg-1µm
Al2O3
Al-Mg-10µm
Al2O3
8
8
8
8
8
65.4
67.4
68.0
67.1
65.4
66.5
67.3
68.8
68.5
69.0
67.4
1.1
74.4
75.1
73.1
75.1
73.6
73.3
73.0
71.9
70.9
71.1
73.2
1.5
66.8
69.4
68.9
69.6
69.8
70.5
68.0
70.2
69.7
68.3
69.1
1.1
67.7
66.1
68.0
65.3
66.5
67.3
67.4
67.1
67.7
67.8
67.1
0.9
62.9
65.6
63.0
61.6
64.5
65.1
62.0
64.9
56.3
61.6
62.8
2.7
100
130
120
120
110
20.25:1
20.25:1
20.25:1
20.25:1
20.25:1
Appendix
Appendix F: Tensile testing specimen dimensions
R = 5.0
∅
∅
= 5.0 ± 0.1
= 8.0
25.0 ± 0.1
Gage Length
26.0
53.0
105.0
26.0
Appendix
Appendix G: Tensile testing raw data
Table G-1: Tensile test results for Phase I.
Al25
Specimen
1
2
3
Average
0.2% Yield
Strength (MPa)
168
168
162
166 ± 4
Ultimate Tensile
Strength (MPa)
173
180
173
175 ± 4
Failure Strain
(%)
14.1
13.2
14.9
14.1 ± 0.8
0.2% Yield
Strength (MPa)
158
155
137
150 ± 11
Ultimate Tensile
Strength (MPa)
162
160
143
155 ± 10
Failure Strain
(%)
15.0
15.2
15.1
15.1 ± 0.1
0.2% Yield
Strength (MPa)
149
147
146
147 ± 1
Al150
Ultimate Tensile
Strength (MPa)
158
159
156
158 ± 1
Failure Strain
(%)
16.2
17.1
17.6
17.0 ± 0.7
Al250
0.2% Yield
Ultimate Tensile
Strength (MPa)
Strength (MPa)
130
136
131
139
135
135
132 ± 2
137 ± 2
Failure Strain
(%)
18.8
19.3
20.0
19.4 ± 0.6
Al350
Ultimate Tensile
Strength (MPa)
112
118
124
118 ± 6
Failure Strain
(%)
23.6
23.8
28.4
25.3 ± 2.8
Al85
Specimen
1
2
3
Average
Specimen
1
2
3
Average
Specimen
1
2
3
Average
Specimen
1
2
3
Average
0.2% Yield
Strength (MPa)
110
114
119
114 ± 5
Appendix
Table G-2: Tensile test results for Phase II.
Al-7
Specimen
1
2
3
Average
0.2% Yield
Strength (MPa)
167
167
166
167 ± 1
Ultimate Tensile
Strength (MPa)
175
175
177
176 ± 1
Failure Strain
(%)
13.1
14.6
14.3
14.0 ± 0.8
Al-10
Specimen
1
2
3
Average
0.2% Yield
Strength (MPa)
146
145
145
145 ± 1
Ultimate Tensile
Strength (MPa)
151
150
150
150 ± 1
Failure Strain
(%)
15.9
14.0
16.8
15.6 ± 1.4
Appendix
Table G-3: Tensile test results for Phase III.
Specimen
1
2
3
Average
Specimen
1
2
3
Average
Specimen
1
2
3
Average
Al-1.6Mg/Al2 O3
0.2% Yield
Ultimate Tensile
Strength (MPa)
Strength (MPa)
225
257
236
266
232
268
231 ± 6
264 ± 6
Failure Strain
(%)
8.8
8.1
9.1
8.7 ± 0.5
Al-2.9Mg/Al2 O3
0.2% Yield
Ultimate Tensile
Strength (MPa)
Strength (MPa)
275
332
273
338
268
380
272 ± 4
350 ± 26
Failure Strain
(%)
4.9
6.3
7.1
6.1 ± 1.1
Al-3.4Mg/Al2 O3
0.2% Yield
Ultimate Tensile
Strength (MPa)
Strength (MPa)
302
380
305
375
300
335
302 ± 3
363 ± 25
Failure Strain
(%)
6.6
6.0
7.1
6.6 ± 0.6
Appendix
Table G-4: Tensile test results for Phase IV.
Specimen
1
2
3
Average
Specimen
1
2
3
Average
Specimen
1
2
3
Average
Specimen
1
2
3
Average
Al-Mg
0.2% Yield
Ultimate Tensile
Strength (MPa)
Strength (MPa)
215
312
214
318
228
329
219 ± 8
320 ± 9
Failure Strain
(%)
12.3
10.9
12.2
11.8 ± 0.8
Al-Mg-0.3µm Al2 O3
0.2% Yield
Ultimate Tensile
Strength (MPa)
Strength (MPa)
232
342
230
334
238
349
233 ± 4
342 ± 7
Failure Strain
(%)
10.7
10.3
12.2
11.1 ± 1.0
Al-Mg-1µm Al2 O3
0.2% Yield
Ultimate Tensile
Strength (MPa)
Strength (MPa)
230
328
214
321
227
330
230 ± 18
332 ± 9
Failure Strain
(%)
7.4
7.7
7.5
8.3 ± 1.1
Al-Mg-10µm Al2 O3
0.2% Yield
Ultimate Tensile
Strength (MPa)
Strength (MPa)
236
293
237
305
214
296
229 ± 13
298 ± 7
Failure Strain
(%)
4.0
5.4
6.0
5.2 ± 1.0
Appendix
400
350
300
Stress (MPa)
250
200
150
100
50
0
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.08
0.1
0.12
0.14
0.08
0.1
0.12
0.14
Strain
(a)
400
350
300
Stress (MPa)
250
200
150
100
50
0
0
0.02
0.04
0.06
Strain
(b)
400
350
300
Stress (MPa)
250
200
150
100
50
0
0
0.02
0.04
0.06
Strain
(c)
Figure G-1: Stress-strain curves of Al25.
Appendix
350
300
Stress (MPa)
250
200
150
100
50
0
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
Strain
(a)
300
250
Stress (MPa)
200
150
100
50
0
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
Strain
(b)
350
300
Stress (MPa)
250
200
150
100
50
0
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
Strain
(c)
Figure G-2: Stress-strain curves of Al85.
0.16
Appendix
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.1
0.12
0.14
0.16
0.1
0.12
0.14
0.16
Strain
(a)
400
350
300
Stress (MPa)
250
200
150
100
50
0
0
0.02
0.04
0.06
0.08
Strain
(b)
400
350
300
Stress (MPa)
250
200
150
100
50
0
0
0.02
0.04
0.06
0.08
Strain
(c)
Figure G-3: Stress-strain curves of Al150.
Appendix
400
350
300
Stress (MPa)
250
200
150
100
50
0
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
Strain
(a)
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.1
0.12
0.14
0.16
0.18
Strain
(b)
400
350
300
Stress (MPa)
250
200
150
100
50
0
0
0.02
0.04
0.06
0.08
Strain
(c)
Figure G-4: Stress-strain curves of Al250.
Appendix
500
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
Strain
(a)
500
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.05
0.1
0.15
0.2
0.25
0.15
0.2
0.25
Strain
(b)
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.05
0.1
Strain
(c)
Figure G-5: Stress-strain curves of Al350.
Appendix
500
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.08
0.1
0.12
0.14
Strain
(a)
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.02
0.04
0.06
Strain
(b)
500
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.02
0.04
0.06
0.08
0.1
0.12
Strain
(c)
Figure G-6: Stress-strain curves of Al-7.
0.14
0.16
Appendix
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.1
0.12
0.14
0.16
0.1
0.12
0.14
0.16
Strain
(a)
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.02
0.04
0.06
0.08
Strain
(b)
400
350
300
Stress (MPa)
250
200
150
100
50
0
0
0.02
0.04
0.06
0.08
Strain
(c)
Figure G-7: Stress-strain curves of Al-10.
Appendix
500
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
Strain
(a)
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.005
0.01
0.015
0.02
0.025
0.03
Strain
(b)
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
Strain
(c)
Figure G-8: Stress-strain curves of Al-1.6Mg/Al2 O3 .
0.1
Appendix
500
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.05
0.06
0.07
0.08
Strain
(a)
600
500
Stress (MPa)
400
300
200
100
0
0
0.01
0.02
0.03
0.04
Strain
(b)
600
500
Stress (MPa)
400
300
200
100
0
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
Strain
(c)
Figure G-9: Stress-strain curves of Al-2.9Mg/Al2 O3 .
0.09
Appendix
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
Strain
(a)
500
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
Strain
(b)
500
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
Strain
(c)
Figure G-10: Stress-strain curves of Al-3.4Mg/Al2 O3 .
0.08
Appendix
500
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
Strain
(a)
500
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.02
0.04
0.06
0.08
0.1
0.12
Strain
(b)
500
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.02
0.04
0.06
0.08
0.1
0.12
Strain
(c)
Figure G-11: Stress-strain curves of Al-Mg.
0.14
Appendix
500
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.02
0.04
0.06
0.08
0.1
0.12
0.08
0.1
0.12
Strain
(a)
500
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.02
0.04
0.06
Strain
(b)
500
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
Strain
(c)
Figure G-12: Stress-strain curves of Al-Mg-0.3µm Al2 O3 .
Appendix
500
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.05
0.06
0.07
0.08
0.09
0.05
0.06
0.07
0.08
0.09
Strain
(a)
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.01
0.02
0.03
0.04
Strain
(b)
500
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.01
0.02
0.03
0.04
Strain
(c)
Figure G-13: Stress-strain curves of Al-Mg-1µm Al2 O3 .
Appendix
500
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0.05
Strain
(a)
500
450
400
350
Stress (MPa)
300
250
200
150
100
50
0
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.04
0.05
0.06
0.07
Strain
(b)
600
500
Stress (MPa)
400
300
200
100
0
0
0.01
0.02
0.03
Strain
(c)
Figure G-14: Stress-strain curves of Al-Mg-10µm Al2 O3 .
Appendix
Appendix H: Coefficient of Thermal Expansion (CTE) Raw Data
Table H-1: CTE values of aluminium (Phase I & II)
Specimen
Al25
Al85
Al150
Al250
1
25.183
26.039
24.497
25.630
2
23.997
25.336
27.828
26.932
3
26.202
26.720
26.433
26.563
Average
25.13 ± 1.10
26.03 ± 0.69
26.25 ± 1.67
26.38 ± 0.67
Specimen
Al350
Al-7
Al-8
Al-10
1
26.053
25.602
26.039
25.476
2
26.412
26.308
25.336
26.208
3
25.086
24.557
26.720
26.261
Average
25.85 ± 0.69
25.49 ± 0.88
26.03 ± 0.69
25.98 ± 0.44
Table H-2: CTE values of Al-Mg/Al2 O3 materials (Phase III)
1
Al-1.6Mg
/Al2 O3
26.644
Al-2.9Mg
/Al2 O3
25.530
Al-3.4Mg
/Al2 O3
25.227
2
26.549
26.884
24.686
3
28.170
27.096
26.418
Average
27.12 ± 0.91
26.50 ± 0.85
25.44 ± 0.89
Specimen
Appendix
Table H-3: CTE values of Al-Mg/Al2 O3 materials (Phase IV)
28.341
Al-Mg-0.05µm
Al2 O3
25.227
Al-Mg-0.3µm
Al2 O3
26.987
Al-Mg-1µm
Al2 O3
27.917
2
27.192
24.686
26.533
26.074
3
27.246
26.418
26.921
25.573
Average
27.59 ± 0.65
25.44 ± 0.89
26.81 ± 0.25
26.52 ± 1.23
Specimen
Al-Mg
1
1
Al-Mg-10µm
Al2 O3
24.447
2
24.354
3
23.755
Average
24.19 ± 0.38
Specimen
[...]... comprised of the following 4 phases: (a) Phase I – Investigate the effect of extrusion temperature on the microstructure and properties of pure Al (b) Phase II – Investigate the effect of extrusion ratio on the microstructure and properties of pure Al (c) Phase III – Investigate the effect of magnesium addition on the incorporation of Al2O3 and properties of Al/Al2O3 composite (d) Phase IV – Investigate the. .. metal-to-metal contact, diffusion occurs across the foil interfaces This process combines the advantages of ease of processing a wide variety of matrix metals, and the control of orientation and volume fraction of the fibers The main problems associated with this process are fiber degradation and thermal expansion mismatch Fiber-matrix interfacial reactions during diffusion bonding can cause degradation of the. .. reinforcement particulates and (b) the limited volume fraction of reinforcement that can be incorporated Settling of reinforcement occurs as a result of density difference between reinforcement particulates and the matrix melt The volume fraction of reinforcement is limited because the viscosity of the melt increases with particle incorporation and becomes non-Newtonian [3] As a result, the power requirements... magnesium contents in the aluminium matrix The optimal magnesium weight fraction was determined and used to process the composites in Phase IV Phase IV investigates the effect of the size of alumina reinforcement on the properties of the composite The samples obtained were characterized for their microstructural, physical and mechanical properties with respect to the effect of different alumina reinforcement. .. properties of the matrix The main difficulty in this process is the removal of the binder used to hold the powder particles together These organic binders often leave residual contamination that causes deterioration of the mechanical properties of the composite The other disadvantages are the: (a) inherent danger when handling large quantities of highly reactive powders, (b) the complexity of the manufacturing... expansion (CTE) – If the composite is to be used in thermal applications, the CTE and thermal conductivity are important The CTE also influences the strength of the composite 4 Compatibility with matrix material – Reaction of the reinforcement with the matrix can severely degrade the properties of the resultant composite 5 Cost – A major reason for using particles as reinforcement is to reduce the cost of. .. reaction products is necessary for obtaining a strong interface, the amount of reaction at the interface must be controlled During the production of MMCs, control of the 18 Literature Research reaction layer thickness and morphology may be difficult Excessive formation of reaction products may be detrimental to the mechanical properties of the composite Heat treatment of particulates before their dispersion... the cracking of materials during primary breakdown from the ingot Extrusion can also reduce particle clustering and create a more uniform reinforcement distribution There is a complex interrelationship between extrusion ratio, working temperature, speed of deformation, and frictional conditions at the die and container wall The selection of optimum process variables for billet size in the present study... modulus and low density In addition, the melting temperature of the fibers has to be higher than that of the matrix, and the fibers are expected to be compatible with the matrix from the points of view of technology and lifetime Continuous fiber MMCs exhibit very good directional properties 12 Literature Research However, the high cost of continuous fiber reinforcement and labor-intensive fabrication routes... dispersion in the melt aids their incorporation by causing desorption of adsorbed gases from the ceramic surfaces Ultrasonic vibrations promote wetting by a similar mechanism to heat treatment In addition, they also supply energy for melt cavitation which facilitates particulate dispersion in the melt From the above considerations, it was decided to investigate the effect of magnesium addition on the incorporation ... ease of processing a wide variety of matrix metals, and the control of orientation and volume fraction of the fibers The main problems associated with this process are fiber degradation and thermal... volume fractions of reinforcement are possible, thus maximizing the improvement of the properties of the matrix The main difficulty in this process is the removal of the binder used to hold the. .. particulates and the matrix melt The volume fraction of reinforcement is limited because the viscosity of the melt increases with particle incorporation and becomes non-Newtonian [3] As a result, the
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