Iridescent chromium coatings and method

Abstract

A method is described for producing an iridescent chromium coating on a zinc-nickel alloy surface containing at least about 8% nickel in the alloy. The method of the invention comprises (A) contacting said surface with an aqueous acidic solution maintained at a temperature of from about 38.degree. C. to about 75.degree. C., wherein the solution comprises trivalent chromium as substantially the only chromium ion present, and a phosphorus acid selected from phosphoric acid, phosphorous acid, hypophosphorous acid and mixtures thereof in an amount effective to provide a solution having a pH of from about 1.0 to about 2.5; and (B) drying the surface. Metal articles having zinc-nickel alloy surfaces containing at least about 8% nickel in the alloy which have been treated in accordance with the method of the invention exhibit the desired iridescent coating and are characterized by improved corrosion resistance.

Dependencies are inferred from the claim text.