| 摘要 |
PROBLEM TO BE SOLVED: To enable the industrially stable production of a zinc-chromium alloy plated steel sheet excellent in corrosion resistance and corrosion resistance after coating without deteriorating its quality by specifying the amt. of hydrogen ions in the surface of the steel sheet to be plated and executing zinc-chromium alloy electroplating while the fluctuation of chromium hydroxide film is suppressed. SOLUTION: The amt. of hydrogen ions in the surface of the steel sheet to be plated is allowed to satisfy hydrogen ion feeding velocity >= hydrogen ion consuming velocity in the vicinity of the surface. For example, it is regulated by the inequality of ([H<+> ]×the distance between the steel sheet and the anode×the relative flow rate)/(the length of an electrolytic cell)>=(0.5×current density)/96500. Then, while the fluctuation of chromium hydroxide film is suppressed, a zinc-chromium alloy layer is formed by electroplating. For example, even in the case zinc-chromium alloy electroplating is continuouslly executed by a horizontal electrolytic cell using an acidic plating soln. contg. Zn<2+> ions, Cr<3+> ions and organic additives, by regulating the flow rate of the plating soln. to 0.5 to 2.5m/sec, the purpose can be attained.
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