Coated steel sheet
A coated steel sheet including a steel sheet and a coating layer provided on at least part of the surface of the steel sheet, in which the coating layer has a predetermined chemical composition in terms of % by mass, and the coating layer has a granular Mg 2 Sn phase-containing structure in an area fraction of from 5 to 65%, and a structure containing a solid solution of Zn and Al, and the granular Mg 2 Sn phase-containing structure is a structure constituted with a Zn phase and a granular Mg 2 Sn phase having a crystal grain size of less than 1 μm dispersed in the Zn phase.
1. A coated steel sheet comprising a steel sheet and a coating layer provided on at least a part of a surface of the steel sheet, wherein:
the coating layer has a chemical composition comprising in terms of % by mass:
Al: from 15% to 60%
Mg: from 0.5% to 8.0%
Sn: from 0.5% to 20.0%
Si: from 0.05% to 1.50%
Bi: from 0% to 5.0%,
In: from 0% to 2.0%,
Ca: from 0% to 3.0%,
Y: from 0% to 0.5%,
La: from 0% to 0.5%,
Ce: from 0% to 0.5%,
Cr: from 0% to 0.25%,
Ti: from 0% to 0.25%,
Ni: from 0% to 0.25%,
Co: from 0% to 0.25%,
V: from 0% to 0.25%,
Nb: from 0% to 0.25%,
Cu: from 0% to 0.25%,
Mn: from 0% to 0.25%,
Sr: from 0% to 0.5%,
Sb: from 0% to 0.5%,
Pb: from 0% to 0.5%,
B: from 0% to 0.5%, and
a balance comprising Zn and impurities, wherein:
the coating layer has a granular Mg 2 Sn phase-containing structure in an area fraction of from 5 to 65%, and a structure containing a solid solution of Zn and Al, and
the granular Mg 2 Sn phase-containing structure is a structure constituted with a Zn phase and a granular Mg 2 Sn phase having a crystal grain size of less than 1 μm dispersed in the Zn phase.
2. The coated steel sheet according to claim 1 , wherein a content of Mg is from 0.5% to 3.0%, and a content of Sn is from 1.0% to 7.5% in terms of % by mass.
3. The coated steel sheet according to claim 1 , wherein a content of Al is from 20% to 60%, a content of Mg is from 1.0% to 2.0%, a content of Sn is from 1.0% to 5.0%, and a content of Si is from 0.05% to 1.0% in terms of % by mass.
4. The coated steel sheet according to claim 1 , wherein a content of Sn and a content of Mg satisfy the following Formula (1):
Mg≤Sn≤2.5×Mg Formula (1)
wherein, in Formula (1), each atomic symbol indicates a content of the element in terms of % by mass.
5. The coated steel sheet according to claim 1 , wherein the area fraction of the granular Mg 2 Sn phase-containing structure is from 20% to 60%.
6. The coated steel sheet according to claim 1 , wherein the area fraction of the granular Mg 2 Sn phase-containing structure is from 30% to 60%.
7. The coated steel sheet according to claim 1 , wherein an area fraction of the structure containing a solid solution of Zn and Al is from 35% to 95%.
8. The coated steel sheet according to claim 1 , wherein the coating layer has a massive MgZn 2 phase with an equivalent circle diameter of 1 μm or more in an area fraction of from 0% to 20%.
9. The coated steel sheet according to claim 1 , wherein the coating layer has a massive MgZn 2 phase with an equivalent circle diameter of 1 μm or more in an area fraction of from 0% to 5%.
10. The coated steel sheet according to claim 1 , wherein the coating layer has a massive Zn phase with an equivalent circle diameter of 2 μm or more in an area fraction of from 0% to 20%.
11. The coated steel sheet according to claim 1 , wherein the coating layer has a massive Zn phase with an equivalent circle diameter of 2 μm or more in an area fraction of from 0% to 10%.
12. The coated steel sheet according to claim 1 , further comprising an interfacial alloy layer with a thickness of from 100 nm to 1.5 μm consisting of an Al—Fe intermetallic compound between the steel sheet and the coating layer.
13. The coated steel sheet according to claim 2 , wherein a content of Al is from 20% to 60%, a content of Mg is from 1.0% to 2.0%, a content of Sn is from 1.0% to 5.0%, and a content of Si is from 0.05% to 1.0% in terms of % by mass.
14. The coated steel sheet according to claim 2 , wherein a content of Sn and a content of Mg satisfy the following Formula (1):
Mg≤Sn≤2.5×Mg Formula (1)
wherein, in Formula (1), each atomic symbol indicates a content of the element in terms of % by mass.
15. The coated steel sheet according to claim 3 , wherein a content of Sn and a content of Mg satisfy the following Formula (1):
Mg≤Sn≤2.5×Mg Formula (1)
wherein, in Formula (1), each atomic symbol indicates a content of the element in terms of % by mass.
16. The coated steel sheet according to claim 2 , wherein the area fraction of the granular Mg 2 Sn phase-containing structure is from 20% to 60%.
17. The coated steel sheet according to claim 3 , wherein the area fraction of the granular Mg 2 Sn phase-containing structure is from 20% to 60%.
18. The coated steel sheet according to claim 4 , wherein the area fraction of the granular Mg 2 Sn phase-containing structure is from 20% to 60%.