Provided is a composition for surface treatment of an Mg-containing galvanized steel sheet comprising a trivalent chromium compound, a carboxylated vinylidene copolymer, and a cross-linking agent. The composition for surface treatment forms a chromium (III) film and is also cross-linked in coating and drying of the surface of a galvanized steel sheet, thereby forming a three-dimensional compact molecular structure. Thus, a galvanized steel sheet coated with the composition has a coating film with high ductility, and can reduce moisture and/or oxygen permeability such that, not only does a worked section have excellent corrosion resistance, but also the occurrence of darkening and/or black dots can be prevented even when exposed to high-temperature and high-humidity environment for a long period of time.

Provided is a composition for surface treatment of an Mg-containing galvanized steel sheet comprising a trivalent chromium compound, a carboxylated vinylidene copolymer, and a cross-linking agent. The composition for surface treatment forms a chromium (III) film and is also cross-linked in coating and drying of the surface of a galvanized steel sheet, thereby forming a three-dimensional compact molecular structure. Thus, a galvanized steel sheet coated with the composition has a coating film with high ductility, and can reduce moisture and/or oxygen permeability such that, not only does a worked section have excellent corrosion resistance, but also the occurrence of darkening and/or black dots can be prevented even when exposed to high-temperature and high-humidity environment for a long period of time.

Provided is a galvanized steel sheet including: a steel sheet comprising a galvanized layer; and a surface coating layer formed on the galvanized layer by using a composition which comprises a trivalent chromium compound, a carboxylated vinylidene copolymer, and a crosslinking agent. The galvanized layer includes Mg.

Provided is a galvanized steel sheet including: a steel sheet comprising a galvanized layer; and a surface coating layer formed on the galvanized layer by using a composition which comprises a trivalent chromium compound, a carboxylated vinylidene copolymer, and a crosslinking agent. The galvanized layer includes Mg.

A material for a gasket, wherein a chromate or non-chromate film, a phenol resin primer layer and a polyol-crosslinkable fluororubber layer are formed on one or both surfaces of a steel plate in this sequence from the side of the steel plate; the polyol-crosslinkable fluororubber layer is a rubber layer obtained by applying a fluororubber composition that comprises fluororubber, a polyol-based cross-linking agent, an amine-based cross-linking accelerator and silica to the phenol resin primer layer, followed by heating; and the amine-based cross-linking accelerator is a tertiary amine or a salt of a tertiary amine obtained by a reaction between a tertiary amine and an acid. Provided is a material for a gasket mounted in an engine of a vehicle that, in the actual use environment, does not suffer rubber peeling in a part where it contacts water or an anti-freezing solution even if the gasket is used in a state where it contacts different types of metals and, in a sealing part around a combustion room, abrasion or ply separation of a rubber layer hardly occurs.