COMPOSITION FOR FORMING BLACK CHEMICAL CONVERSION COATING

摘要

PROBLEM TO BE SOLVED: To provide a composition for forming a chemical conversion coating used for forming a black chemical conversion coating having high corrosion resistance and high designing properties on the surface of zinc or zinc alloy without using harmful hexavalent chromium compound, and to provide a method for forming the black chemical conversion coating. SOLUTION: The composition for forming the black chemical conversion coating for zinc or zinc alloy is composed of an aqueous solution of pH 1 to 4 satisfying the following conditions (1) to (5): (1) containing a heat-reaction product obtained by reacting a tervalent chromium compound with carboxylic acids in an amount of 0.1 to 10 g/L in terms of a chromium metal content; (2) containing the oxygen acids of phosphorous added after the formation of the heat-reaction product in an amount of 0.1 to 10 g/L in terms of a phosphorous element content; (3) containing a compound including at least one kind of metal selected from the group consisting of nickel and cobalt in an amount of 0.1 to 10 g/L in terms of a metal content; (4) containing an organic sulfur compound in an amount of 0.01 to 5 g/L in terms of a sulfur element content; and (5) containing nitric acid ions in an amount of≥2 mols to 1 mol of the chromium metal. COPYRIGHT: (C)2009,JPO&INPIT