METHOD OF PRODUCING A STEEL SHEET PLATED WITH ZN-MG ALLOY SUPERIOR BOTH IN PLATING ADHESION AND CORROSION RESISTANCE, AND STEEL SHEET PLATED WITH THE SAME

摘要

A plated steel sheet is produced by an electroplating in a plating bath of about 350 to 500 DEG C containing a chloride of Zn, a chloride of Mg and one, two or more of chlorides of Na, K and Li, with a plating current density ranging between about 20 and 350 A/dm<2>. The Zn-Mg alloy plated steel sheet superior both in plating adhesion and corrosion resistance has a plating layer formed on at least one surface thereof in an amount of about 10 to 60 g/m<2>, and by electroplating in a bath of a fused salts, the plating layer containing about 1 to 35 wt% of Mg, about 0.5 to 25 wt% of mean value of Fe and the balance substantially Zn and incidental inclusions. The Fe content in the plating layer has such a gradient that its concentration is greatest at the interface between the plating layer and the steel sheet and progressively decreases towards the surface of the plating layer opposite to the steel sheet where the Fe content is substantially zero. The plated steel sheet may further have a chromate treatment layer formed on the plating layer, with or without an organic coating film formed on the chromate treatment layer.