Anodizing
The formation of an oxide coating by anodizing might be used to improve the wear resistance of certain materials. Usually, the anodizing process is applied to, zinc magnesium aluminium & their alloys. In anodizing, the base metal is built an anode on which oxide layers are built.
Anodizing aluminium is simply a method of building up a much thicker oxide coating than may be obtained by exposure to air. The alumilite procedure developed by the Aluminium Company of America utilizes sulfuric acid as an electrolyte for anodizing. The films developed are transparent, thicker and more porous than those generated by other electrolytes. The surface porosity develops coating soft. The porosity is eliminated or reduced by treating with boiling water which modified porous alumina into monohydrate (Al2O3H2O) which causes an increase in volume and seals the pores. Aircraft parts such as hydraulic pistons, gears, guide tracks, screws, cams, swivel joints and friction locks are built of hard coated aluminium alloys.
The production of hard water resistant surface by anodizing has very much extended the uses of magnesium and its alloys. Flash anodic coatings are frequently used as a base for print adherence.
Anodizing zinc generate a coating which contain greater resistance to wear than chromate films. Anodic zinc coatings are utilized for cartridge cases, wire-screen cloth, air place propeller blades, and refrigerator shelves.