Aluminum Anodizing is an electrolytic process used to increase the thickness of the natural oxide layer on the surface of aluminum parts. Anodizing increases corrosion resistance and wear resistance, and provides better adhesion for paint primers and resins than bare metal. Anodic films can also be used for a number of cosmetic effects, either with thick porous coatings that can absorb dyes or with thin transparent coatings that add interference effects to reflected light.
Sulfuric acid is the most widely used solution to produce anodized coating. Coatings of moderate thickness 1.8 to 25 microns are known as Type II, as named by MIL-A-8625, while coatings thicker than 25 microns are known as Type III, hardcoat, or engineered anodizing.