A galvanized steel sheet according to one aspect of the present invention comprises: a base steel sheet; and a Zn-Al-Mg-based plating layer provided on at least one surface of the base steel sheet, wherein the Zn-Al-Mg-based plating layer may include a surface modified region enriched with cerium (Ce) on a surface layer side of the Zn-Al-Mg-based plating layer.

A galvanized steel sheet according to one aspect of the present invention comprises: a base steel sheet; and a Zn-Al-Mg-based plating layer provided on at least one surface of the base steel sheet, wherein the Zn-Al-Mg-based plating layer may include a surface modified region enriched with cerium (Ce) on a surface layer side of the Zn-Al-Mg-based plating layer.

The invention relates to a method for producing a silane-modified silicate. In order to obtain optimal corrosion protection properties, a silane compound according to the invention is at least partially hydrolyzed and/or condensed in the presence of a silicate compound at a pH value greater than or equal to 8 and then a pH value less than or equal to 7 is set by adding acid. The invention further relates to an aqueous acidic passivation composition for metal substrate coated with the passivation composition.

The invention relates to a method for producing a silane-modified silicate. In order to obtain optimal corrosion protection properties, a silane compound according to the invention is at least partially hydrolyzed and/or condensed in the presence of a silicate compound at a pH value greater than or equal to 8 and then a pH value less than or equal to 7 is set by adding acid. The invention further relates to an aqueous acidic passivation composition for metal substrate coated with the passivation composition.

A sliding member includes, on a surface of a metal substrate, a surface-treated layer including a zinc-electroplated layer, a chemical conversion-treated layer, and a topcoat layer sequentially stacked on the metal substrate. The chemical conversion-treated layer includes chromium and oxygen. The topcoat layer includes at least one material selected from the group consisting of a silica compound, acrylic resin, polyurethane resin, epoxy resin, phenol resin, and melamine resin. A method of manufacturing the sliding member includes a step of forming, on a surface of the chemical conversion-treated layer, the topcoat layer including at least one material selected from the group consisting of a silica compound, acrylic resin, polyurethane resin, epoxy resin, phenol resin, and melamine resin.

A sliding member includes, on a surface of a metal substrate, a surface-treated layer including a zinc-electroplated layer, a chemical conversion-treated layer, and a topcoat layer sequentially stacked on the metal substrate. The chemical conversion-treated layer includes chromium and oxygen. The topcoat layer includes at least one material selected from the group consisting of a silica compound, acrylic resin, polyurethane resin, epoxy resin, phenol resin, and melamine resin. A method of manufacturing the sliding member includes a step of forming, on a surface of the chemical conversion-treated layer, the topcoat layer including at least one material selected from the group consisting of a silica compound, acrylic resin, polyurethane resin, epoxy resin, phenol resin, and melamine resin.

A trivalent-chromium chemical conversion coating from which substantially no hexavalent chromium is released. The trivalent-chromium chemical conversion coating is one formed on the surface of a zinc or zinc-alloy deposit. In a brine spray test, the chemical conversion coating has unsusceptibility to corrosion (time required for white-rust formation) of 96 hours or longer. The chemical conversion coating has a hexavalent-chromium concentration less than 0.01 μg/cm.sup.2 in terms of metal atom amount. The amount of hexavalent chromium released after 30-day standing in a thermo-hygrostatic chamber at a temperature of 80° C. and a humidity of 95% (amount of hexavalent chromium released when the coating is immersed in 100° C. water for 10 minutes) is smaller than 0.05 μg/cm.sup.2.

A trivalent-chromium chemical conversion coating from which substantially no hexavalent chromium is released. The trivalent-chromium chemical conversion coating is one formed on the surface of a zinc or zinc-alloy deposit. In a brine spray test, the chemical conversion coating has unsusceptibility to corrosion (time required for white-rust formation) of 96 hours or longer. The chemical conversion coating has a hexavalent-chromium concentration less than 0.01 μg/cm.sup.2 in terms of metal atom amount. The amount of hexavalent chromium released after 30-day standing in a thermo-hygrostatic chamber at a temperature of 80° C. and a humidity of 95% (amount of hexavalent chromium released when the coating is immersed in 100° C. water for 10 minutes) is smaller than 0.05 μg/cm.sup.2.

The present application is directed to an aqueous passivation composition for the treatment of zinc or zinc alloy coatings, said composition having a pH of from 6.5 to 9 and comprising, based on the weight of the composition: a) at least one base polymer selected from acrylic polymers and non-ionic polyurethane polymers present in an amount of from 5 to 60 wt. % of; b) trivalent Cr(III) ions, present in an amount of from 0.1 to 2.5 wt. %, calculated as Cr; c) ascorbic acid; d) at least one aluminum compound present in an amount of from 0.1 to 2.5 wt. %; and, e) at least one finely divided wax present in the composition in an amount of up to 10 wt. %; wherein said composition is substantially free of nitrate anions and is substantially free of hexavalent chromium (Cr(VI)).

The present application is directed to an aqueous passivation composition for the treatment of zinc or zinc alloy coatings, said composition having a pH of from 6.5 to 9 and comprising, based on the weight of the composition: a) at least one base polymer selected from acrylic polymers and non-ionic polyurethane polymers present in an amount of from 5 to 60 wt. % of; b) trivalent Cr(III) ions, present in an amount of from 0.1 to 2.5 wt. %, calculated as Cr; c) ascorbic acid; d) at least one aluminum compound present in an amount of from 0.1 to 2.5 wt. %; and, e) at least one finely divided wax present in the composition in an amount of up to 10 wt. %; wherein said composition is substantially free of nitrate anions and is substantially free of hexavalent chromium (Cr(VI)).