Method for preparing corrosion-resistant zinc-cobalt surfaces

Abstract

The present invention relates to compositions and methods for providing a corrosion-resistant coating on a zinc-cobalt alloy surface said surface with a hexavalent chromium-containing treatment solution. In a preferred embodiment, the solution comprises: (a) about 2 to about 30 g/l of CrO.sub.3 ; (b) 0 to about 25 g/1 of dichromate ion such that the total Cr.sup.+6 is about 1 to about 35 g/l; (c) about 0.5 to about 20 g/l of NH.sub.4.sup.+ ; and (d) about 5 to about 30 g/l of formate ion. The solution additionally comprises: (e) about 2 to about 25 g/l of Cl.sup.- ; and has a pH controlled by the addition of HCl or NaOH of about 0.8 to about 2.5. The solution is substantially-free of sulfate, chlorate and nitrate. In one embodiment, the formate is optional and low levels of Cr.sup.+6 are employed.

Dependencies are inferred from the claim text.