Mechanics of aircraft materials 2 cdio

Nonferrous Aircraft Metals

Heat Treatment of Nonferrous Aircraft Metals

Mechanics of Aircraft Materials

Department of Aerospace Engineering – Faculty of Transportation Engineering

Dr Ly Hung Anh

N ONFERROUS A IRCRAFT M ETALS

“nonferrous” metals: all metals which have elements other than iron as their base or principal constituent.

A LUMINUM

Aluminum is one of the most widely used metals in modern aircraft construction.

Properties of pure aluminum:

white lustrous metal

second in the scale of malleability

sixth in ductility

ranks high in its resistance to corrosion.

high strength to weight ratio

comparative ease of fabrication

low melting temperature of 1,250 °F

nonmagnetic

excellent conductor.

tensile strength of about 13,000 psi 4

magnesium and silicon

Alloys in which substantial percentages of copper are used are more susceptible to corrosive action.

The total percentage of alloying elements is seldom more than 6 or 7 percent in the wrought alloys.

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A LUMINUM A LLOYS

The tensile strength may be raised to as high as 65,000 psi or to within the strength range of structural steel.

Aluminum alloys, although strong, are easily worked because they are malleable and ductile.

They may be rolled into sheets as thin as 0.0017 inch or

They may be rolled into sheets as thin as 0.0017 inch or drawn into wire 0.004 inch in diameter.

Most aluminum alloy sheet stock used in aircraft

construction range from 0.016 to 0.096 inch in thickness; however, some of the larger aircraft use sheet stock

which may be as thick as 0.356 inch.

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C LASSIFICATIONS OF A LUMINUM A LLOYS

Casting alloys: suitable for casting in sand, permanent mold, or die castings.

Wrought alloys: may be shaped by rolling, drawing, or forging.

The wrought alloys are the most widely used in aircraft

The wrought alloys are the most widely used in aircraft

C ASTING A LUMINUM A LLOYS

2 types:

The physical properties are determined by the alloying elements and cannot be changed after the metal is cast.

The alloying elements make it possible to heat treat the casting to produce the desired physical properties.

Identification: by a letter preceding the alloy number.

addition of zinc in casting alloy 214: A214.

heat treatment of casting alloy 355: T355.

Casting methods:

sand mold

permanent mold

M OLD C ASTINGS

Mold castings:

pouring molten metal into a previously prepared mold

allowing the metal to solidify or freeze

removing the part

Molds:

Molds:

Sand: sand casting.

Metals (cast iron): permanent mold casting

Properties: metal flowing under the force of gravity alone.

Examples: casting alloys 112 and 212.

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P ERMANENT M OLD C ASTING

Properties: fewer openings (called porosity) than in sand castings.

Using for obtain

higher mechanical properties

better surfaces

better surfaces

more accurate dimensions.

Two specific types :

Permanent metal mold with metal cores.

Semi-permanent types containing sand cores.

Examples: Alloys 122, A132, and 142

Applications: used in internal combustion engines. 10

D IE C ASTING

Die castings used in aircraft are usually aluminum or magnesium alloy.

Aluminum alloys: stronger

Magnesium alloys: lighter A die casting:

A die casting:

forcing molten metal under pressure into a metallic die

allowing it to solidify

the die is opened and the part removed

Die castings are used where relatively large production of a given part is involved.

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F IRST G ROUP

The second digit indicates specific alloy modifications.

0: indicate no special control over individual impurities

1-9: indicate the number of controls over individual impurities in the metal.

The last two digits: indicate the hundredths of 1 percent above the original 99 percent designated by the first

S ECOND G ROUP

The second digit in the alloy designation indicates alloy modifications.

if the second digit is zero, it indicates the original alloy,

digits 1 through 9 indicate alloy modifications.

The last two of the four digits in the designation identify

The last two of the four digits in the designation identify the different alloys in the group.

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E FFECT OF A LLOYING E LEMENTS

Copper

It gives the alloy excellent mechanical characteristics

It especially facilitates machining in the quenched state

It improves the creeping strength as well as the resistance to high temperatures

It increases the alloy’s aptitude for surface treatments

It decreases the corrosion resistance

It makes welding difficult

It reduces the capacity of the alloy to be deformed

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E FFECT OF A LLOYING E LEMENTS

It forms alloys insensitive to structural hardening

It forms alloys having an excellent corrosion resistance

It can be easily worked on.

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P ROPERTIES OF A LUMINUM A LLOYS

1000 series:

99 percent aluminum or higher

excellent corrosion resistance

high thermal and electrical conductivity

low mechanical properties

low mechanical properties

excellent workability

major impurities: Iron and silicon

2000 series

Solution heat treatment

optimum properties equal to mild steel

poor corrosion resistance unclad

Its best known alloy is 2024 18

P ROPERTIES OF A LUMINUM A LLOYS

3000 series

generally non-heat treatable

percentage of manganese: effective at 5 percent

most popular is 3003, which is of moderate strength and has good working characteristics.

4000 series

lower melting temperature

primary use is in welding and brazing

respond to a limited amount of heat treatment.

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P ROPERTIES OF A LUMINUM A LLOYS

5000 series

good welding and corrosion resistant characteristics

high temperatures (over 150 °F) or excessive cold working will increase susceptibility to corrosion.

heat-treatable alloys of very high strength

usually has copper and chromium added

principal alloy of this group is 7075 20

H1 (plus one or more digits) — strain hardened only

H2 (plus one or more digits) — strain hardened and partially annealed

H3 (plus one or more digits) — strain hardened and stabilized

The digit following the designations H1, H2, and H3 indicates

M AGNESIUM

Magnesium is the world’s lightest structural metal.

Properties:

silvery white material

weighing only two-thirds as much as aluminum

insufficient strength in its pure state for structural uses

insufficient strength in its pure state for structural uses

highest strength to weight ratio in alloying state.

widely distributed in nature than any other metal.

can be obtained from such and from sea

high thermal conductivity

in large sections: not burn until the melting point of 1,204 °F

in dust and fine chips: ignited easily.

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M AGNESIUM A LLOYS

Magnesium obtained from

ores: dolomite and magnesite

sea water

underground brines

waste solutions of potash

waste solutions of potash

Magnesium alloying elements: aluminum, manganese, and zinc.

Identification:

Designated by a letter of the alphabet, with the number 1 indicating high purity and maximum corrosion resistance.

by the Dow Chemical Company: Downmetal J or M

By the American Magnesium Corporation: AM240C 24

M AGNESIUM A LLOYS P ROPERTIES

Good casting characteristics

Subject to such treatments as annealing, quenching, solution heat treatment, aging, and stabilizing

Sheet and plate magnesium are annealed at the rolling mill

Solution heat treatment: to get high tensile strength and maximum ductility

Aging: to castings following heat treatment to get high hardness and yield strength

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M AGNESIUM A LLOYS A PPLICATIONS

Wing panels: weigh 18 percent less than standard aluminum panels, and have flown hundreds of satisfactory hours

Nose wheel doors

Flap cover skin

Aileron cover skin

Oil tanks

Floorings

Fuselage parts, wingtips, engine nacelles, instrument panels, radio masts

Hydraulic fluid tanks, oxygen bottle cases, ducts, and

T ITANIUM

Titanium, in appearance, is similar to stainless steel.

Properties:

elasticity, density, and elevated temperature strength: between aluminum and stainless steel

melting point of from 2,730 °F to 3,155 °F

melting point of from 2,730 °F to 3,155 °F

low thermal conductivity

low coefficient of expansion

light, strong, and resistant to stress corrosion cracking

60 percent heavier than aluminum and about 50 percent lighter than stainless steel

yield strength drops rapidly above 800 °F

nonmagnetic and has an electrical resistance 28

T ITANIUM A LLOYS

Titanium alloying elements: Iron, molybdenum, and chromium

Production: by quench harden and age harden

The addition of these metals also adds ductility.

The fatigue resistance of titanium is greater than that of

The fatigue resistance of titanium is greater than that of aluminum or steel.

Some of the base alloys of titanium are quite hard.

Heat treating and alloying do not develop the hardness of titanium to the high levels of some of the heat-treated

alloys of steel.

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T ITANIUM A LLOYS A PPLICATIONS

Turbine housings and liners

Miscellaneous hardware for turbine engines. 30

BASIC TYPES OF CRYSTALS

excellent bend ductility

strong both cold and hot

vulnerable to contamination

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BASIC TYPES OF CRYSTALS

C (combined alpha and beta for compromise performances):

strong when cold and warm, but weak when hot

good bendability

moderate contamination resistance

moderate contamination resistance

excellent forgeability

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high electrical and heat conductivity

high electrical and heat conductivity

malleable and ductile

corroded by salt water but not affected by fresh water

ultimate tensile strength of copper varies greatly:

25,000 psi for cast copper

40,000 to 67,000 psi for cold rolled copper

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C OPPER A LLOYS

One of the most successful of all the copper base alloys

Composition: about 97 percent copper, 2 percent beryllium, and sufficient nickel to increase the percentage of elongation

Properties:

the tensile strength rising from 70,000 psi in the annealed state to 200,000 psi in the heat-treated state

Resistance to fatigue and wear

C OPPER A LLOYS

B RASS

Composition: zinc and small amounts of aluminum, iron, lead, manganese, magnesium, nickel, phosphorous, and tin.

Brass with a zinc content of 30 to 35 percent is very ductile.

Brass containing 45 percent zinc has relatively high strength.

Muntz metal:

Muntz metal:

composed of 60 percent copper and 40 percent zinc.
excellent corrosion resistant qualities in salt water.

strength can be increased by heat treatment (50,000 psi in cast).
used in making bolts and nuts, parts that come in contact with salt

C OPPER A LLOYS

The true bronzes have up to 25 percent tin.

In aircraft: less than 11 percent are most useful.

about 95 percent copper, 3 percent silicon, and 2 percent manganese, zinc, iron, tin, and aluminum

high strength

great corrosion resistance

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C OPPER A LLOYS

ALUMINUM BRONZE

Composition: contain up to 16 percent of aluminum

(usually 5 to 11 percent), and other metals, such as iron, nickel, or manganese.

Properties:

good tearing qualities

good tearing qualities

great strength and hardness

resistance to both shock and fatigue

N ICKEL A LLOYS

M ONEL

Monel is the leading high nickel alloy.

Composition: 68 percent nickel, 29 percent copper, 0.2 percent iron, 1 percent manganese, and 1.8 percent of other elements.

Properties:

Properties:

cannot be hardened by heat treatment

adaptable to casting and hot or cold working

tensile strength of 80,000 psi

Applications:

gears and chains to operate retractable landing gears

exhaust manifolds , carburetor needle valves and sleeves.

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N ICKEL A LLOYS

Inconel and stainless steel are similar in appearance and are frequently found in the same areas of the engine.

Composition: approximately 80 percent nickel, 14

percent chromium, and small amounts of iron and other elements.

Properties:

high strength

high working temperature

corrosion resistance under extremely high temperature conditions.

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HEAT TREATMENT OF NONFERROUS METALS

NONFERROUS METALS

A LUMINUM A LLOYS HEAT TREATMENT IDENTIFICATION

O — Soft or annealed condition

H — Strain hardened condition

W — Solution heat treated, unstable temper

T — Treated to produce stable tempers other than O, or H

T2 — Annealed (cast products only)

T3 — Solution heat treated and then cold worked

T3 — Solution heat treated and then cold worked

T4 — Solution heat treated

T5 — Artificially aged only

T6 — Solution heat treated and then artificially aged

T7 — Solution heat treated and then stabilized

T8 — Solution heat treated, cold worked, and then artificially aged

T9 — Solution heat treated, artificially aged, and then cold worked

T10 — Artificially aged and then cold worked 44

A LUMINUM A LLOY H EAT T REATMENT

2 types:

solution heat treatment

precipitation heat treatment

Heat treatment process:

Heating to a predetermined temperature.

Heating to a predetermined temperature.

Soaking at temperature for a specified length of time.

Rapidly quenching to a relatively low temperature.

Aging or precipitation hardening either spontaneously at

room temperature, or as a result of a low temperature thermal treatment.

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S OLUTION H EAT T REATMENT

The temperatures used for solution heat treating vary with different alloys and range from 825 °F to 980 °F.

The time at temperature: soaking time

measured from the time the coldest metal reaches the minimum limit of the desired temperature range

varies, depending upon the alloy and thickness, from 10 minutes for thin sheets to approximately 12 hours for heavy forgings

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Q UENCHING

Quenching is used to prevent or retard immediate reprecipitation.

Three distinct quenching methods:

Cold Water Quenching

Hot Water Quenching

Hot Water Quenching

Spray Quenching

Cold Water Quenching

quenched in a cold water bath

temperature before quenching should not exceed 85 °F

using a sufficient quantity of water keeps the temperature rise under 20 °F

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Q UENCHING

Hot Water Quenching

quenched in hot or boiling water

minimizes distortion and alleviates cracking

temperature of the quench water does not critically affect the resistance to corrosion of the forging alloys

Spray Quenching

quenched in high velocity water sprays

minimizes distortion and alleviates quench cracking

The aluminum alloys are in a comparatively soft state immediately after quenching from a solution heat-treating temperature

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P RECIPITATION H EAT T REATMENT

Aging or precipitation hardening are applied to obtain the maximum strength of aluminum alloys.

Precipitation hardening process:

Precipitation of the soluble constituents from the super -saturated solid solution

Strength is due to the uniform distribution of a finely

Strength is due to the uniform distribution of a finely

dispersed submicroscopic precipitate and its effects upon the crystal structure of the alloy

Increase the strength and hardness of the material

Decreases in the ductile properties

Aging:

Natural aging: 4 or 5 days at room temperature

Artificially aging: temperatures ranging from 250 °F to 375 °F.

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