In North America, chromic acid anodizing is frequently referred to as Type I anodizing as designated by the MIL-A-8625 standard. It is also covered in the AMS 2470 and the ASTM B580 specifications. Chromic acid anodizing enhances the corrosion resistance of aluminum parts and produces a thin opaque film that is soft, ductile, non-conductive, and to a degree self-healing. A typical thickness is usually 0.00005-0.0001 inches. Chromic acid anodize may be applied as a pretreatment before painting to enhance adhesion and it is harder to dye than sulfuric acid anodize. The big advantage of chromic acid anodize has over other anodizing processes is that it does not lower the fatigue strength of the aluminum or damage the base material if it is entrapped in lap joints or blind holes. After chromic acid anodize the solution may be sealed in either hot water or sodium dichromate solutions.
