Aqueous treating solution for forming black trivalent-chromium chemical conversion coating on zinc or zinc alloy and method of forming black trivalent-chromium chemical conversion coating

Abstract

A treating solution for forming on a surface of either zinc or a zinc alloy a hexavalent-chromium-free trivalent-chromium chemical conversion coating which has an even black appearance and satisfactory corrosion resistance. The treating solution has a long treating-bath life. Also provided is a method of forming a black trivalent-chromium chemical conversion coating. The aqueous treating solution, which is for forming a black trivalent-chromium chemical conversion coating on zinc or a zinc alloy, contains trivalent chromium ions, a phosphoric ester and/or phosphorous ester, and a sulfur compound. The method is a method of chemically treating zinc or a zinc alloy which comprises using the aqueous treating solution to chemically treat the zinc or zinc alloy at a solution temperature of 10-60° C., whereby a black trivalent-chromium chemical conversion coating is formed on the zinc or zinc alloy. Furthermore provided is a coated zinc or zinc alloy metal which comprises zinc or a zinc alloy and, formed thereon, a black trivalent-chromium chemical conversion coating formed by a chemical treatment with the aqueous treating solution.

Dependencies are inferred from the claim text.