Quasicrystal-containing plated steel sheet and method for producing quasicrystal-containing plated steel sheet

1. A quasicrystal-containing plated steel sheet comprising:

a plating layer positioned on at least one surface of a steel sheet; and

an alloy layer positioned at an interface between the plating layer and the steel sheet and composed of an Al—Fe intermetallic compound,

wherein a chemical composition of the plating layer contains, in atom %,

Zn: 28.5% to 50%,

Al: 0.3% to 12%,

La: 0% to 3.5%,

Ce: 0% to 3.5%,

Y: 0% to 3.5%,

Ca: 0% to 3.5%,

Sr: 0% to 0.5%,

Si: 0% to 0.5%,

Ti: 0% to 0.5%,

Cr: 0% to 0.5%,

Fe: 0% to 2%,

Co: 0% to 0.5%,

Ni: 0% to 0.5%,

V: 0% to 0.5%,

Nb: 0% to 0.5%,

Cu: 0% to 0.5%,

Sn: 0% to 0.5%,

Mn: 0% to 0.2%,

Sb: 0% to 0.5%,

Pb: 0% to 0.5%, and

the balance: Mg and impurities, and

the plating layer includes, in order from the steel sheet side,

a first plating layer which is composed of a structure containing an MgZn phase, an Mg phase, and a quasicrystal phase, and

a second plating layer which is positioned on the first plating layer and is composed of a structure containing an Mg 51 Zn 20 phase, a Zn phase, and a quasicrystal phase.

2. The quasicrystal-containing plated steel sheet according to claim 1 ,

wherein a chemical composition of the plating layer contains, in atom %,

Zn: 32% to 40%,

Al: 2% to 5%,

Ca: 1% to 2.5%, and

the balance: Mg and impurities,

the chemical composition satisfies

atomic ratio Zn/Al=7.5 to 18 and

atomic ratio Ca/Al=0.4 to 1.1, and

a maximum grain size of the second plating layer is 1 μm or less in terms of circle equivalent diameter.

3. The quasicrystal-containing plated steel sheet according to claim 1 ,

wherein when the plating layer is viewed in a cross section in which a sheet thickness direction and a cutting direction are parallel to each other,

the MgZn phase of the first plating layer is configured by crystal grains having a circle equivalent diameter of 1 μm or more, and

the quasicrystal phase of the first plating layer is configured by a structure grown in the thickness direction of the plating layer.

4. The quasicrystal-containing plated steel sheet according to claim 1 , wherein when the plating layer is viewed in a cross section in which a sheet thickness direction and a cutting direction are parallel to each other,

an area of a structure in which the maximum grain size of the second plating layer is 1 μm or less in terms of circle equivalent diameter is 90% or more with respect to a cross-sectional area of the entire second plating layer.

5. The quasicrystal-containing plated steel sheet according to claim 1 , wherein when the plating layer is viewed in a cross section in which a sheet thickness direction and a cutting direction are parallel to each other,

an area of the MgZn phase of the first plating layer is 10% to 70% with respect to a cross-sectional area of the entire first plating layer.

6. The quasicrystal-containing plated steel sheet according to claim 1 , wherein the second plating layer does not contain an Mg phase.

7. The quasicrystal-containing plated steel sheet according to claim 1 , wherein an average value of Vickers hardness measured at 10 gf of the second plating layer is 250 to 350 Hv.

8. The quasicrystal-containing plated steel sheet according to claim 1 ,

wherein the alloy layer contains at least any of Fe 5 Al 2 and Al 3.2 Fe as the Al—Fe intermetallic compound, and

a thickness of the alloy layer is 10 nm to 200 nm.

9. A method for producing the quasicrystal-containing plated steel sheet according to claim 1 , the method comprising:

a plating step of disposing a plating alloy in a molten state on at least one surface of a steel sheet, a chemical composition of the plating alloy containing, in atom %,

Zn: 28.5% to 50%,

Al: 0.3% to 12%,

La: 0% to 3.5%,

Ce: 0% to 3.5%,

Y: 0% to 3.5%,

Ca: 0% to 3.5%,

Sr: 0% to 0.5%,

Si: 0% to 0.5%,

Ti: 0% to 0.5%,

Cr: 0% to 0.5%,

Fe: 0% to 2%,

Co: 0% to 0.5%,

Ni: 0% to 0.5%,

V: 0% to 0.5%,

Nb: 0% to 0.5%,

Cu: 0% to 0.5%,

Sn: 0% to 0.5%,

Mn: 0% to 0.2%,

Sb: 0% to 0.5%,

Pb: 0% to 0.5%, and

the balance: Mg and impurities;

a first cooling step of cooling the plating alloy in a molten state to a temperature range of 330° C. or lower at an average cooling rate of 10° C./sec or less to form a plating layer on the surface of the steel sheet;

a temperature increasing and holding step of increasing a temperature of the plating layer into a temperature range of 350° C. to 400° C. at a temperature increasing rate range of 10 to 50° C./sec after the first cooling step and holding the temperature for 5 to 30 seconds; and

a second cooling step of cooling the plating layer at a cooling rate of 20° C./sec or more after the temperature increasing and holding step.

10. The method for producing a quasicrystal-containing plated steel sheet according to claim 9 ,

wherein the plating step is performed by a hot-dip plating method, and

after the steel sheet is pulled up from a hot-dip plating bath, the first cooling step is continuously performed.

11. The method for producing a quasicrystal-containing plated steel sheet according to claim 9 ,

wherein a chemical composition of the plating alloy in a molten state contains, in atom %,

Zn: 32% to 40%,

Al: 2% to 5%,

Ca: 1% to 2.5%, and

the balance: Mg and impurities, and

the chemical composition satisfies

atomic ratio Zn/Al=7.5 to 18 and

atomic ratio Ca/Al=0.4 to 1.1.