Patent ID: 8337641

Claim:
A treatment solution for forming a black hexavalent chromium-free chemical conversion coating film on zinc or zinc alloy, the solution comprising: a trivalent chromium ion; a chelating agent capable of forming a water soluble complex with the trivalent chromium ion; one or more metal ions selected from the group consisting of cobalt ion, nickel ion and iron ion; formic acid or a salt thereof used as a buffer in a hydrogen-ion concentration; and one or more inorganic acid ions selected from the group consisting of a phosphate ion, chlorine ion, nitrate ion and sulfate ion, wherein the content of the trivalent chromium ion is in the range of 0.5 to 15 g/L, the content of the chelating agent is in the range of 1 to 40 g/L, the content of the formic acid or salt thereof is in the range of 1 to 20 g/L and the content of the inorganic acid ions is in the range of 5 to 80 g/L.