PRODUCTION OF ZINC-NICKEL ALLOY ELECTROPLATED STEEL SHEET GOOD IN APPEARANCE AFTER CHEMICAL CONVERSION

PROBLEM TO BE SOLVED: To obtain a Zn-Ni electroplated steel sheet free from the generation of unevenness in chemical conversion and good in appearance after chemical conversion by regulating the temp. directly before contact of a Zn-Ni electroplated steel sheet to be brought into contact with an aq. soln. contg. H3 PO4 , H2 PO4 or HPO4 to a fixed temperature in a plating post treating stage. SOLUTION: Diectly before a plating post treating tank in which an aq. soln. contg. one or more kinds among H3 PO4 , H2 PO4 and HPO4 and a plated steel sheet are brought into contact with, a means of regulating the temp. of a steel sheet is provided, and treating is executed so as to regulate the sheet temp. to a fixed temperature. The temp. of the plated steel sheet in time of its impragnation into the plating post treating tank is preferably regulated to 30 to 70 deg.C. In the case the temp. of the plated steel sheet at the time of the impragnation is less than 30 deg.C, the quantity to be reacted in the post treating tank reduces, and the effect of preventing unevenness in the chemical conversion is insufficient, therefore, it is not preferable. On the other hand, in the case of >70 deg.C, etching reaction in the plating layer rapidly occurs to cause unevenness in the reaction and to be easy to cause defects in the appearance, therefore, it is not preferable.