anodize, anodiing, nhôm anot, Anodise process anodize nhôm, alumium anodize The formation of the oxides take place by the migration of Al3+ ion away from the metal towards the electrolyte interfere, while simultaneously O2 ions from the electrolyte move in the opposite direction
aluminium anodizing Aluminium Oxide Film aluminium(III) oxide (alumina): Occurs naturally with crystalline polymorphic phase Al2O3 as a barrier layer These films is very thin (0.01 μm) Anodizing Process Apply voltage and current with electrolyte solution to produce aluminium oxide film Advantages of Anodizing • Corrosion resistance • Wear resistance • Paint adhesion: Aluminum oxide film is a chemically active surface for painting • Color dyeing (taking advantage of the unique porous oxide film) Misconception: Does not increase mechanical strength of material But can increase hardness to prevent abrasion Chart of Aluminium alloy Anodizing Technology An electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts The process is called anodizing because the part to be treated forms the anode electrode of an electrical circuit Jigs, Racks and Fixture Function of Jigs and racks: To hold the part securely during transfer between process tanks To provide contacts with the work that will safety conduct enough current from the source to the part to provide uniform coating To provide adequate draining of the work, leaving no pocket of residue solution trapped in the component Jigs, Racks and Fixture Material for anodizing jigs and racks Aluminium Titanium Advantages Low initial cost Ease of fabrication High Electric conductivity Advantages Good Strength Good durability Chemical inertness Disadvantages High initial cost Requires specialist repair facilities Need periodic removal of H2 embrittlement *Good racking materials are 6061 and 2024 More limited current carrying capacity than Al Disadvantages Progressive weakening Less robustness in handing term Jigs, Racks and Fixture Guidelines for anodizing jigs and racks considering: The location of contact point Make sure critical surface meet to thickness requirement Use racks of a less readily avoidable alloy than the work Alternatively, mask off with tape Do not anodize parts of difference alloy at the same time Even vigorous, agitation is essential to the process, so check that part is firmly held on the jig before process Aluminium Anodizing process Cleaning Mild Alkaline cleaner Alkaline Etching Etching additives and scale inhibitors Desmut Desmutting Anodizing Neutralization Anodising Neutralization Dyeing Dyestuff Sealing Hot Sealing Water rinse *2 between each step This diagram does not represent the process of Anodising Pretreatment for Anodising Product type Oxide Film Other Contaminants Extrusions As extruded: air formed film Heat treated: a thicker film richer in magnesia formed if Mg is present Cu, Fe and Mn oxides in strong heat treated alloys As extruded air‐formed film If heat treated a film rich in MgO when Mg present Air formed film from annealing, but think if annealed in a controlled atmosphere Thicker oxide film present heat treated alloys Tubes Sheet Cutting saw lubricant Drilling or cutting lubricant if fabricated Forming lubricant if used Drawing lubricant is present Forming lubricant if tubes are subject to bending Lubricant residue from rolling and cut‐off shears Lubricant from pressing and drawing Forgings Thickned oxide film from heat treatment Residual forging lubricant may contain C or MoS2 Casting Oxide film formed during cooling A silicon‐rich surface layer often present Residual die dressing and/or lubricant Sand residue ‐ Graphite 10 Dyeing of Anodic Coating Given the color and performance specifications are known as anodizing coating, which are organic dye complexes containing metal ions 43 Dyeing: Mechanism The dyeing process involve an adsorption mechanism and a chemical bonding reaction Color anodic films are absorbed by the anodic coating Dyestuffs combine with aluminium oxide to form a stable co-valent bond cause to high light-fastness 44 Dyeing of Anodic Coating Normal range of dyeing operation: Dye concentration: 0.5-5.0 g/l Temperature: 60o-70oC pH: 5.0-6.0 Time: 5-15 Aluminium color shade Dyeing Control: – Oxide layer Control – Time Control – Temperature Control – Concentration Control – pH Control 45 Electrolytic Coloring (EC) The deposition of metallic particles in the pores of an anodic coating by the passage of an electric current through a solution containing metallic salt (i.e cobalt, nickel, tin and copper) EC is carried out using alternating current which means that condition within the coating are alternately anodic and cathodic The deposition reaction is: MeSO4 Me2+ + SO42Me2+ + 2e- Me0 46 Method of Sealing Work pieces after anodizing has a sticky feel and highly absorbent surface that readily stain Hot sealing is used hot rinse as a dry-off , the following parameters are significant: Water temp Sealing time pH of the water 47 Mechanism of Hot Sealing • Traditional only hot water (DI) Hydolysis of Alumina to form crystallised Boehmite 48 Mechanism of Hot Sealing The diffusion of hydroxyl ions into the anodic coating, as rate of sealing is non-linear 49 Effect Factors of Hot Sealing Electron micrographs of the surface of film sealed following time in water at 100 oC a) b) 10 c) 30 d) 24 hr 50 Effect Factors of Hot Sealing Effect of sealing time on the weight loss in acidified solution sulphite sealing test 51 Effect Factors of Hot Sealing Effect of sealing temp on the weight loss in acidified solution sulphite sealing test 52 Effect Factors of Hot Sealing Ionic impurity in hot sealing 53 Additive of Sealing Bath The use of metal salt to the seal bath, mainly nickel or cobalt are used for preventing “bleeding-out” of dyes during sealing Increasing tolerance for silica and other dissolved salts 54 Cold Sealing -Technically called “Impregnation Sealing” - Impregnation process at 25-30 oC -The fluoride in the solution prepares the porous anodized layer and then deposit as a fluoro-aluminium to impregnate NiF2 + Al2O3 + 3H2O NiAl2(OH)6F2 -Process is slow A warm water rinse after the sealing will accelerate the impregnation process 55 Quality Test Method of Anodizing Coating thickness Dye stain test Weight loss test Sunlight fastness UV fastness Heat fastness 56 Thank you for your attention 57