Steel sheet with hot dip galvanized zinc alloy coating and process to produce it
Steel strip provided with a hot dip galvanized zinc alloy coating layer, in which the coating of the steel strip is carried out in a bath of molten zinc alloy, the zinc alloy in the coating consisting of: 0.3-2.3 weight % magnesium; 0.6-2.3 weight % aluminum; optional <0.2 weight % of one or more additional elements; unavoidable impurities; the remainder being zinc in which the zinc alloy coating layer has a thickness of 3-12 μm.
1. Steel strip provided with a hot dip galvanized zinc alloy coating layer, wherein the zinc alloy consists of:
magnesium;
aluminium;
optional <0.2 weight % of one or more additional elements selected from the group consisting of Pb, Sb, Ti, Ca, Mn, Sn, La, Ce, Cr, Ni, Zr and Bi;
unavoidable impurities;
the remainder being zinc;
wherein the magnesium and aluminum content in the zinc alloy layer is selected from a member of the group consisting of:
1.6-1.9 weight % aluminium and 1.4-1.7 weight % magnesium;
wherein the zinc alloy coating layer has a thickness of 3-10 μm,
wherein silicon content in the zinc alloy layer is below 0.0010 weight %.
2. Steel strip provided with a hot dip galvanized zinc alloy coating layer according to claim 1 , wherein the zinc alloy coating layer has a thickness of 3-8 μm.
3. Steel strip provided with a hot dip galvanized zinc alloy coating layer according to claim 2 , wherein the one or more additional elements are present in the zinc alloy coating, each <0.02 weight %.
4. Steel strip provided with a hot dip galvanized zinc alloy coating layer according to claim 2 , wherein the amount of aluminium in weight % is within 0.3 weight % of the amount of magnesium in weight %.
5. Steel strip provided with a hot dip galvanized zinc alloy coating layer according to claim 1 , wherein the zinc alloy coating layer has a thickness of 3-7 μm.
6. Steel strip provided with a hot dip galvanized zinc alloy coating layer according to claim 5 , wherein the one or more additional elements are present in the zinc alloy coating, each <0.02 weight %.
7. Steel strip provided with a hot dip galvanized zinc alloy coating layer according to claim 5 , wherein the amount of aluminium in weight % is within 0.3 weight % of the amount of magnesium in weight %.
8. Steel strip provided with a hot dip galvanized zinc alloy coating layer according to claim 1 , wherein the one or more additional elements are present in the zinc alloy coating, each <0.02 weight %.
9. Steel strip provided with a hot dip galvanized zinc alloy coating layer according to claim 8 , wherein the amount of aluminium in weight % is within 0.3 weight % of the amount of magnesium in weight %.
10. Steel strip provided with a hot dip galvanized zinc alloy coating layer according to claim 1 , wherein the amount of aluminium in weight % is within 0.3 weight % of the amount of magnesium in weight %.
11. Process for making the steel strip provided with a hot dip galvanized zinc alloy coating layer of claim 1 comprising hot dip galvanising a steel strip with a zinc alloy coating layer, in which the coating of the steel strip is carried out in a bath of molten zinc alloy, wherein the zinc alloy coating layer consists of:
magnesium;
aluminium;
less than 0.0010 weight % of silicon;
optional <0.2 weight % of one or more additional elements selected from the group consisting of Pb, Sb, Ti, Ca, Mn, Sn, La, Ce, Cr, Ni, Zr and Bi;
unavoidable impurities;
the remainder being zinc, wherein the magnesium and aluminum content in the zinc alloy coating layer is selected from a member of the group consisting of:
1.6-1.9 weight % aluminium and 1.4-1.7 weight % magnesium;
wherein the zinc alloy coating layer has a thickness of 3-10 μm,
wherein silicon content in the zinc alloy layer is below 0.0010 weight %.
12. Process according to claim 11 , wherein the temperature of the bath of molten zinc is kept between 380° C. and 550° C.
13. Process according to claim 11 , wherein the temperature of the steel strip before entering the bath of molten zinc alloy is between 380° C. and 850° C.
14. Process according to claim 11 , wherein the steel strip enters the bath of molten zinc alloy having a speed higher than 9 meters per minute.
15. Process according to claim 11 , wherein the temperature of the bath of molten zinc is kept between 420° C. and 480° C.
16. Process according to claim 11 , wherein the temperature of the steel strip before entering the bath of molten zinc alloy is between the temperature of the bath of molten zinc alloy and 25° C. above the bath temperature.
17. Process according to claim 11 , wherein the steel strip enters the bath of molten zinc alloy having a speed higher than 15 meters per minute.
18. Process according to claim 11 , wherein the steel strip enters the bath of molten zinc alloy having a speed higher than 30 meters per minute.
19. Steel strip provided with a hot dip galvanized zinc alloy coating produced with the method according to claim 11 .
20. Automotive part manufactured from a steel strip according to claim 1 .
21. Steel strip provided with a hot dip galvanized zinc alloy coating layer according to claim 1 , wherein the one or more additional elements are present in the zinc alloy coating, each <0.01 weight %.