Patent ID: 7018521

Claim:
A method of forming a colored bright anodized coating on a surface of an aluminum alloy article, where said alloy contains more than three percent by weight magnesium; immersing said surface to be anodized in an aqueous acid solution at a temperature below about 100° C., said solution comprising one or more mineral acids selected from the group consisting of, by weight, ten to twenty percent sulfuric acid, ten to thirty percent nitric acid, and forty to eighty percent phosphoric acid until the magnesium content in said surface is reduced to less than three percent and to produce a glossy surface; anodizing said surface in an aqueous sulfuric acid bath containing 100 to 200 grams of sulfuric acid per liter of bath at a temperature in the range of 18 to 25° C. and at a current density in the range of about 3 A/ft 2 to 10 A/ft 2 that produces a desired thickness of a clear anodized layer suitable for color finishing; and coloring said clear anodized layer to produce said colored coating.