Zn—Al—Mg coated steel sheet, and method of producing Zn—Al—Mg coated steel sheet
AssigneeNippon Steel Corporation
InventorsShigeru Hashimoto, Makoto Nakazawa
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Abstract
Provided is a Zn—A—Mg coated steel sheet having a plated layer including from 4 to 22% by mass of Al, from 1.0 to 6.5% by mass of Mg, from 0.001 to 1.000% by mass of Si, as well as Zn and impurities as the balance, wherein the structure of the plated layer contains an Al primary crystal, the Al primary crystal including: a cellular dendrite-shaped first Al primary crystal and a second axis spacing of from 0.5 to 2.0 μm; a minute equi-axed dendrite-shaped second Al primary crystal and a second axis spacing of from 0.5 to 2.0 μm; and a petal-shaped third Al primary crystal with a principal axis length of from 0.5 to 3.0 μm and a ternary eutectic structure of Al, Zn, and Mg2Zn11 as a structure other than the Al primary crystal.
Claims5
A Zn—Al—Mg coated steel sheet, comprising a plated layer comprising from 4 to 22% by mass of Al, from 1.0 to 6.5% by mass of Mg wherein Mg is ½ or less of Al in terms of % by mass, from 0.001 to 1.000% by mass of Si, and Zn and impurities as the balance,
- wherein the structure of the plated layer comprises:
- an Al primary crystal, the Al primary crystal comprising:
- a cellular dendrite-shaped first Al primary crystal with an area rate of from 30 to 70% and a second axis spacing of from 0.5 to 2.0 μm;
- a minute equi-axed dendrite-shaped second Al primary crystal with a principal axis length of from 5 to 10 μm and a second axis spacing of from 0.5 to 2.0 μm;
- and a petal-shaped third Al primary crystal with a principal axis length of from 0.5 to 3.0 μm, wherein a total area rate of the minute equi-axed dendrite-shaped second Al primary crystal and the petal-shaped third Al primary crystal is from 30 to 70%,
- wherein the area rate of the Al primary crystal is determined from a surface of the plated layer;
- and
- a ternary eutectic structure of Al, Zn, and Mg2Zn11 as a structure other than the Al primary crystal.
A method of producing a Zn—A—Mg coated steel sheet, the method comprising:
- plating, on at least one side of a steel sheet, molten zinc comprising from 4 to 22% by mass of Al, from 1.0 to 6.5% by mass of Mg wherein Mg is ½ or less of Al in terms of % by mass, from 0.001 to 1.000% by mass of Si, and Zn and impurities as the balance, and
- heating the steel sheet plated with the molten zinc to any temperature of a range from 30° C. higher than a solidification initiation temperature of an Al primary crystal to 520° C., and then cooling to a temperature of 370° C. at a cooling rate of 500° C./sec or more, and securing an overall heat-transfer coefficient during cooling of from 1000 to 3000 W/(m2·K).
Dependencies are inferred from the claim text.