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SURFACE-TREATED ZINC-COATED STEEL SHEET EXCELLENT IN PLANAR-PART CORROSION RESISTANCE, BLACKENING RESISTANCE, AND APPEARANCE AND CORROSION RESISTANCE AFTER PRESS FORMING ; AND AQUEOUS SURFACE TREATMENT FLUID FOR ZINC-COATED STEEL SHEET
SURFACE-TREATED ZINC-COATED STEEL SHEET EXCELLENT IN PLANAR-PART CORROSION RESISTANCE, BLACKENING RESISTANCE, AND APPEARANCE AND CORROSION RESISTANCE AFTER PRESS FORMING ; AND AQUEOUS SURFACE TREATMENT FLUID FOR ZINC-COATED STEEL SHEET
An aqueous surface treatment fluid containing a water-soluble zirconium compound, a water-dispersible fine particulate silica, a silane coupling agent, a vanadic acid compound, a phosphoric acid compound, a nickel compound, and an acrylic resin emulsion at a specific ratio. A surface-treated zinc-coated steel sheet produced by using the treatment fluid is constituted of a zinc-coated steel sheet and a surface treatment film formed on the surface of the sheet which contains a zirconium compound, fine particulate silica, a component resulting from a silane coupling agent, a vanadic acid compound, a phosphoric acid compound, a nickel compound, and an acrylic resin at a specific ratio and has a Zr build-up of 10 to 200mg/m2. The surface-treated zinc-coated steel sheet is excellent in planar-part corrosion resistance, blackening resistance, and appearance and corrosion resistance after press forming, though it is free from chromate.
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