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AssigneeDipsol Chemicals Co., Ltd.
InventorsKatsuhide Oshima, Shigemi Tanaka, Manabu Inoue, Tomitaka Yamamoto
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A processing solution for forming a hexavalent chromium free, corrosion resistant trivalent chromate conversion film on zinc or zinc alloy plating layers comprises: trivalent chromium and oxalic acid in a molar ratio ranging from 0.5/1 to 1.5/1, wherein the trivalent chromium is present in the form of a water-soluble complex with oxalic acid; and cobalt ions, which do not form a hardly soluble metal salt with oxalic acid and are stably present in the processing solution without causing any precipitation; wherein the solution reacts with zinc when bringing it into contact with the zinc or zinc alloy plating to form a hexavalent chromium free, corrosion resistant, trivalent chromate conversion film containing zinc, chromium, cobalt, oxalic acid and silicon on the plating. The film is quite thin, free of any hexavalent chromium, has corrosion resistance identical to or higher than that achieved by the conventional hexavalent chromium-containing film and can be formed using a processing solution having a quite low concentration.
A processing solution for forming a hexavalent chromium free, corrosion resistant trivalent chromate conversion film on zinc or zinc alloy plating layers, which comprises:
A hexavalent chromium free, corrosion resistant, trivalent chromate conversion film containing zinc, trivalent chromium, cobalt and oxalic acid and formed on zinc or zinc alloy plating layers, wherein the mass ratio of trivalent chromium to (trivalent chromium+zinc)[Cr/(Cr+Zn)] is not less than 15/100, the mass ratio of cobalt to (trivalent chromium+cobalt)[Co/(Cr+Co)] ranges from 5/100 to 40/100 and the mass ratio of the oxalic acid to (trivalent chromium+oxalic acid)[oxalic acid/(Cr+oxalic acid)] ranges from 5/100 to 50/100.
A hexavalent chromium free, corrosion resistant, trivalent chromate conversion film containing zinc, trivalent chromium, cobalt and oxalic acid and formed on zinc or zinc alloy plating layers, wherein the mass ratio of trivalent chromium to (trivalent chromium+zinc)[Cr/(Cr+Zn)] is not less than 20/100 to 60/100, the mass ratio of cobalt to (trivalent chromium+cobalt)[Co/(Cr+Co)] ranges from 10/100 to 40/100 and the mass ratio of the oxalic acid to (trivalent chromium+oxalic acid)[oxalic acid/(Cr+oxalic acid)] ranges from 10/100 to 50/100.
A method for forming a hexavalent chromium free, corrosion resistant, trivalent chromate conversion film comprising:
A method for forming a hexavalent chromium free, corrosion resistant, trivalent chromate conversion film comprising the steps of:
Dependencies are inferred from the claim text.