What is the difference between a sulfuric acid anodize, hard anodize, and conversion coating?
In the sulfuric acid anodizing process, the aluminum workpiece is placed in an acid-based electrolyte. An electric current is then passed through the part. During the oxidation process, the workpiece is coated with a hard, porous oxide layer. Organic coatings or dyes of various colors can thus be applied to the aluminum outside surface. The primary difference between the sulfuric acid anodize and hard anodizing processes are the operating temperature and the current density at which the process occurs. Hard anodizing produces a heavier coating with better wear properties than a sulfuric acid anodize. The conversion coating, also known as chrome phosphate or chrome oxide (yellow chrome), is a process that treats the metal surface as a result of chemical attack occurring when the metal is immersed in, or sprayed with, various solutions. This finish provides protection and good adhesion, but would typically be used as a base for another final finish.
