Treatment solution for forming of black trivalent chromium chemical coating on zinc or zinc alloy and method of forming black trivalent chromium chemical coating on zinc or zinc alloy

摘要

A treatment solution that is used to form a chemical coating of trivalent chromium free of hexavalent chromium having uniform black appearance and good corrosion resistance on the surface of zinc or zinc alloy and that attains prolongation of treatment bath lifetime; and a method of forming a black trivalent chromium chemical coating on the surface of zinc or zinc alloy. There is provided a treatment solution for forming of a black trivalent chromium chemical coating on zinc or zinc alloy, comprising trivalent chromium ions, a chelating agent capable of forming a water-soluble complex with trivalent chromium, zinc ions, a sulfur compound and phosphite ions.