Stabilized trivalent chromium passivate composition and process

Abstract

An aqueous acidic solution and process for treating metal surfaces, particularly zinc and zinc alloy surfaces, for depositing a passivate film to impart improved corrosion resistance thereto. The solution contains effective amounts of chromium ions substantially all of which are present in the trivalent state, hydrogen ions to provide a pH of about 1.2 to about 2.5, an oxidizing agent, a stabilizing agent comprising a mixture of 1--hydroxy ethylidene--1,1 diphosphonic acid and citric acid as well as the bath soluble and compatible salts thereof present in an amount effective to stabilize the oxidizing agent and pH of the aqueous acidic solution, and at least one additional metal ion selected from the group consisting of iron, cobalt, nickel, molybdenum, manganese, aluminum, lanthanum, cerium, lanthanide mixture as well as mixtures thereof. The treating solution may optionally further contain a bath soluble and compatible silicate compound, halide ions, a carboxylic acid or salt thereof and a wetting agent.

Dependencies are inferred from the claim text.