Patent ID: 10202676

Abstract:
A hot-dip Zn alloy plating layer is formed on a surface of a base steel sheet by immersing the base steel sheet in a hot-dip Zn alloy plating bath containing Al and Mg. An aqueous solution containing a polyatomic ion including Si4+ and/or a polyatomic ion including Cr6+ is then contacted with a surface of the hot-dip Zn alloy plating layer. All of the aqueous solution coating the surface of the hot-dip Zn alloy plating layer is removed with a squeeze roller. The aqueous solution contains the polyatomic ion in a concentration of 0.01 g/L or more in terms of atom of Si and Cr. A surface temperature of the hot-dip Zn alloy plating layer when the aqueous solution is contacted with the surface of the hot-dip Zn alloy plating layer is 100° C. or above and equal to or less than a solidifying point of the plating layer.