Hard anodizing aluminum makes aluminum retain the basic advantages of aluminum while providing greatly improved wear, heat resistance, and corrosion resistance.
Aluminum parts are wired or placed into pinch racks and attached to a copper bar which helps conduct electricity. Only the surfaces that require hard anodize treatment are exposed to the processing. All other surfaces or holes are protected using plugs or liquid maskant.
The parts are then lifted by hoist and lowered into the tanks. Parts are alkaline cleaned, etched and then deoxidized; this ensures that the parts are clean, free of foreign contaminants and ready to for the anodize coating. Parts are then immersed into the sulfuric acid anodize tank and charged with an electrical current, producing a dense, hard layer of aluminum oxide both on and in the aluminum surface.
The coating is thick by normal anodizing standards, ranging typically from 1 to 3 mils, or more if desired. Hard anodizing penetrates the base metal in a ratio equal to the build up on the surface. This oxide coating can be harder than case hardened steel and provides excellent abrasion resistance and durability.
Coating color varies from colorless to light brown to jet black depending upon the alloy composition and coating thickness.
Surface Finish Surface roughness increases as the coating thickness increases; typical increases are 10 to 20 micro inches for wrought alloys and 50 to 100 micro inches for castings. Parts can be used as is or honed, lapped or ground where fine finishes are required.