Process for forming a black oxide on aluminum alloys and a solution therefor

A process for forming a black oxide on a surface of an aluminum-containing metal, the process comprising the steps of:

• cleaning the surface of the aluminum-containing metal so as to remove oils and other contaminants that would otherwise hinder formation of the black oxide on the surface;
• and
• without first anodizing the surface, treating the surface of the aluminum-containing metal to a solution that develops the black oxide, the solution comprising a catalyst consisting essentially, per liter, of about 5 to about 12 grams of sodium phosphate dibasic, about 5 to about 12 grams of sodium benzoate and about 0.5 to about 1 gram of sodium molybdate dihydrate;
• distilled water containing chlorides, sulfates and bicarbonates of sodium salts, and a substance for maintaining the pH of the solution at a level sufficient to promote a reaction between the surface of the aluminum-containing metal and the chlorides, sulfates and bicarbonates of sodium salts at a temperature of about 80.degree. C. to about 90.degree. C.