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 Si.sup.4+ and/or a polyatomic ion including Cr.sup.6+ 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.

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 Si.sup.4+ and/or a polyatomic ion including Cr.sup.6+ 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.

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 one of or two or more of polyatomic ions selected from the group consisting of a polyatomic ion including V.sup.5+, a polyatomic ion including Si.sup.4+, and a polyatomic ion including Cr.sup.6+ is then contacted with a surface of the hot-dip Zn alloy plating layer. The aqueous solution contains the polyatomic ion in a concentration of 0.01 g/L or more in terms of one of or two or more of atoms selected from the group consisting of V, Si, and Cr.

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 one of or two or more of polyatomic ions selected from the group consisting of a polyatomic ion including V.sup.5+, a polyatomic ion including Si.sup.4+, and a polyatomic ion including Cr.sup.6+ is then contacted with a surface of the hot-dip Zn alloy plating layer. The aqueous solution contains the polyatomic ion in a concentration of 0.01 g/L or more in terms of one of or two or more of atoms selected from the group consisting of V, Si, and Cr.

A surface-treated steel material includes a coating film formed on a surface of a steel material through a plating layer. The plating layer is obtained by immersing the steel material in a galvalume bath containing Mg. In the surface-treated steel material, the coating film is formed using a coating composition containing a coating film-forming resin, a cross-linking agent, a predetermined vanadium compound, and trimagnesium phosphate. The vanadium compound is a compound satisfying a predetermined electrical conductivity. The content of the vanadium compound is limited to a specified amount with respect to 100 mass % of the total of the coating film-forming resin solids and the cross-linking agent solids. The vanadium compound has a specified pH, and the content of the trimagnesium phosphate is a specified amount with respect to 100 mass % of the total of the coating film-forming resin solids and the cross-linking agent solids.

A surface-treated steel material includes a coating film formed on a surface of a steel material through a plating layer. The plating layer is obtained by immersing the steel material in a galvalume bath containing Mg. In the surface-treated steel material, the coating film is formed using a coating composition containing a coating film-forming resin, a cross-linking agent, a predetermined vanadium compound, and trimagnesium phosphate. The vanadium compound is a compound satisfying a predetermined electrical conductivity. The content of the vanadium compound is limited to a specified amount with respect to 100 mass % of the total of the coating film-forming resin solids and the cross-linking agent solids. The vanadium compound has a specified pH, and the content of the trimagnesium phosphate is a specified amount with respect to 100 mass % of the total of the coating film-forming resin solids and the cross-linking agent solids.

Provided is an insulative coating processing liquid with which an insulative coating can be obtained. The insulative coating processing liquid contains: at least one phosphate selected from the group consisting of Mg, Ca, Ba, Sr, Zn, Al, and Mn; and two or more types of colloidal silicas having different mean particle diameters, wherein the total contained amount of the colloidal silicas in terms of the SiO.sub.2 solid content is 50-120 parts by mass with respect to 100 parts by mass of the solid content of the phosphate, a mean particle diameter ratio expressed as r.sub.i+1/r.sub.i is not lower than 1.5 when the mean particle diameters of the colloidal silicas are represented in an ascending order, and a mass ratio expressed as w.sub.i+1/(w.sub.i+1+w.sub.i) is 0.30-0.90 when the masses of the colloidal silicas in terms of the SiO.sub.2 solid content are represented in an ascending order of the respective mean particle diameters.

A method for the manufacture of a substrate provided with a chromium VI-free and a cobalt-free passivation by the application of a first acidic passivation and a second alkaline passivation, containing a silane-modified and/or a siloxane modified silicate, with which an improved protection against corrosion is achieved, an aqueous, acidic composition for passivating and a passivated substrate, and a device for applying the passivation.

A method for the manufacture of a substrate provided with a chromium VI-free and a cobalt-free passivation by the application of a first acidic passivation and a second alkaline passivation, containing a silane-modified and/or a siloxane modified silicate, with which an improved protection against corrosion is achieved, an aqueous, acidic composition for passivating and a passivated substrate, and a device for applying the passivation.

A method includes providing a workpiece with at least one surface having an anodized aluminum coating and a trivalent chromium sealant. The at least one surface of the workpiece is submerged in a post-treatment sealant solution for 0.5 to 20 minutes. The sealant composition consists essentially of a corrosion inhibitor, an organic complexing agent, and an oxidant.