MOLTEN Al-Zn-BASED PLATED SHEET STEEL, SURFACE-TREATED STEEL PLATE, COATED STEEL PLATE, AND METHOD FOR MANUFACTURING MOLTEN Al-Zn-BASED PLATED SHEET STEEL

Abstract

To provide a molten Al-Zn-based plated sheet steel with excellent plating adhesiveness at a bending-back part even when a plating adhesion amount is large.SOLUTION: The present invention relates to a molten Al-Zn-based plated sheet steel, on which a plating layer having a composition containing 40-70 mass% of Al and 0.5-3.0 mass% of Si, and Zn and inevitable impurities at a remainder, is formed. The plating layer has a dendrite gap mainly containing dendrite made of Al primary crystal and Al-Zn eutectic crystal. The thickness X (μm) of the plating layer and the Vickers hardness HV0.01 of the Al primary crystal satisfy the following expressions (1) and (2). HV0.01≤-4X+205...(1) X≥23...(2)SELECTED DRAWING: Figure 4

Claims

[Claim 1] A hot-dip Al-Zn plated steel sheet is formed on which a plating layer has been formed having a composition containing Al: 40 to 70% by mass, Si: 0.5 to 3.0% by mass, and Mg: 5% by mass or less, with the remainder being Zn and unavoidable impurities. The aforementioned plating layer has dendrites mainly composed of primary Al crystals and dendritic gaps containing Al-Zn eutectic crystals. The thickness X (μm) of the plating layer and the Vickers hardness HV of the primary Al crystal. ０．０１ A hot-dip Al-Zn plated steel sheet characterized in that it satisfies the following relationships (1) and (2). HV ０．０１ ≦-4X+205 ・・・(1) X ≥ 23 ... (2) [Claim 2] The hot-dip Al-Zn plated steel sheet according to claim 1, characterized in that, in a bending test in accordance with JIS G 3322 (2019), a 180-degree tight-fit bend is performed with a width of 125 mm without inserting a plate between the inner bends, the tight-fit bend is then returned to its original shape and smoothed, and then adhesive tape is applied to the surface of the unbent portion that was on the inside during the tight-fit bend. When the tape is peeled off in a direction perpendicular to the bend line of the unbent portion, the maximum width of the peeled plating layer attached to the adhesive tape in a direction perpendicular to the bend line is 1 mm or less. [Claim 3] A surface-treated steel sheet characterized by having a chemical conversion coating formed on a molten Al-Zn plated steel sheet according to claim 1 or 2. [Claim 4] A painted steel sheet characterized by having a coating film formed directly or via an intermediate layer on a molten Al-Zn plated steel sheet according to claim 1 or 2. [Claim 5] A process of forming a plating layer with a plating thickness X (μm) per side on a base steel sheet using a plating bath having a composition containing Al: 40-70% by mass, Si: 0.5-3.0% by mass, and Mg: 5% by mass or less, with the remainder being Zn and unavoidable impurities, The process comprises a step of reheating the steel sheet on which the plating layer has been formed. A method for manufacturing a hot-dip Al-Zn plated steel sheet, characterized in that, when the maximum temperature reached by the steel sheet during reheating is T°C and the cooling time from T°C to 100°C is y (hr), the following relationships (2), (3), and (4) are satisfied. X ≥ 23 ... (2) 150 ≤ T ≤ 300 ... (3) 0.5 ≤ y ≤ 24 ... (4)

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