PRE-HOT DIP Zn-Mg-Al BASED ALLOY PLATED STEEL SHEET EXCELLENT IN CORROSION RESISTANCE IN CUT EDGE FACE

摘要

PROBLEM TO BE SOLVED: To improve the corrosion resistance of a cut edge face in a plated steel sheet by controlling the contents of Mg and Al in a pre-hot dip galvanizing based plating layer to specified ranges and moreover incorporating small amounts of Ti and B therein. ;SOLUTION: The compsn. of a plating layer in a hot dip Zn-Mg-Al based alloy plated steel sheet is composed of, by weight, 1 to 4% Mg, 4 to 10% Al, and the balance Zn with inevitable impurities. Or, 0.002 to 0.1% Ti and 0.001% to 0.045% B are moreover incorporated therein. Mg promotes the formation of Mg-contg. Zn based corrosion products high in protecting properties on the plating layer and reduces the corrosion rate of the plating layer itself. Moreover, a part of the corrosion products flows into the surface of the steel base in the cut edge face to suppress the corrosion of the steel base. Al in the plating layer hardly elutes from the plating layer, and Zn-Al based corrosion products are formed on the lower layer of the Zn based corrosion products high in fluidity. By the addition of Ti and B, the formation of a Zn11Mg2 phase damaging the surface appearance can be suppressed.;COPYRIGHT: (C)2000,JPO