Electrolytic chromate bath for zinc-based plated steel sheet and method for producing electrolytic chromate-treated zinc-based plated steel sheet excellent in corrosion resistance, fingerprint resistance and chrome elution resistance

摘要

The present invention discloses an electrolytic chromate bath for zinc-based galvanized steel and a method for producing an electrolytic chromate treated zinc-based galvanized steel sheet having excellent corrosion resistance, fingerprint resistance and chromium elution resistance. At least one member selected from the group consisting of hexavalent chromium ions in the range of 1 to 50 g / 1 in terms of metal Cr, and 0.1 to 2.0 g / 1 in the form of trivalent chromium ions, divalent nickel ions and divalent cobalt ions; 0.1 to 20 g / 1, silica sol containing 50 to 300 g / 1 in terms of its solid content, 0.05 to 1.0 g / 1 in terms of PO ₄^3- and 1 to 50 g / 1 for sulfate ions, and further trivalent chromium The ratio of the ion concentration / total chromium ion concentration is less than 0.1, the silica sol solid content concentration / trivalent chromium ion concentration ratio is more than 70, the pH is 2.5 ~ 3.8 range, characterized in that the electrolytic chromate zinc Less manufacturing method of plated steel sheet Among the steel sheets subjected to the zinc plating on one side used as a cathode, said electrolytic chromate bath, the bath is characterized in that the electrolytic chromate treatment under the conditions of a current density of 30 ~ 70 ℃ 1 ~ 50A / dm ^2.