Method for providing a Zn—Al—Mg coating, and such coating

Patent metadata

Field	Value
Publication number	US-11306382-B2
Application number	US-201716318229-A
Country	US
Kind code	B2
Filing date	Jul 20, 2017
Priority date	Jul 20, 2016
Publication date	Apr 19, 2022
Grant date	Apr 19, 2022

Abstract

A Zn—Al—Mg coating on a steel strip. Specific amounts of Mg and Al are chosen, in a relationship wherein the amount of Al is higher than the amount of Mg. Also provided is a method for providing a steel strip having a Zn—Al—Mg coating provided by hot dip coating with a coating bath, wherein the thickness of the coating is controlled using gas knifes above the coating bath.

First claim

The invention claimed is:

1. A steel strip having a Zn—Al—Mg coating provided by hot dip coating, wherein the coating has a composition consisting of:
1.1-1.4 weight % magnesium;
1.9-2.3 weight % aluminium;
optional <0.3 weight % of Sn, Bi, Sb, Ln, Ce, Ti, Sc, Sr and/or B in total;
the remainder consisting of zinc and unavoidable impurities;
wherein the Al and Mg contents satisfy the relationship:
Al (in weight %) >1.28 Mg (in weight %)+0.25 with the proviso that if Al is 2.0 weight % then Mg may be 1.4 weight %,
wherein the coating weight of a one-sided coating layer is 35 to less than 45 g/m 2 , and
wherein the coating does not contain binary (Zn+MgZn 2 ) microstructures,
wherein the coating has an absence of a visible beach defect;

wherein the strip has a roughness Ra<1.5 μm before entering a coating bath for the hot dip coating,
wherein the coated steel strip is made by a process comprising controlling the thickness of the coating using gas knifes above a coating bath that provides the alloy for the coating and wherein Z is a value in a range of 5 to 8 mm that meets an equation Z<0.6 e 0.064CW , wherein Z is the distance between each gas knife and the steel strip in mm, and wherein CW is the weight of the one-sided coating layer in g/m 2 and wherein each said gas knife has a distance above the coating bath of at most 500 mm.

2. The steel strip according to claim 1 , wherein the coating weight on each side of the metal strip is 40 to less than 45 g/m 2 and no surface defects are present at all.

3. The steel strip according to claim 2 , wherein Z is in a range from 5 to 8 mm and wherein each said gas knife has a distance above the coating bath of at most 400 mm.

4. The steel strip according to claim 2 wherein the coated steel strip has a length between 1000 and 4000 m and the coating is homogeneous.

5. The steel strip according to claim 1 , wherein the coating weight on each side of the metal strip 35 to less than 40 g/m 2 , and no surface defects are present at all, wherein Z is the distance between each gas knife and the steel strip in mm, and wherein Z is in a range from 5 to 7.5 mm, wherein the gas knifes have a distance above the bath of at most 400 mm.

6. The steel strip according to claim 1 , wherein Z is in a range from 5 to 7 mm.

7. The steel strip according to claim 2 , wherein the coating has a composition in which 2.0-2.3 weight % aluminium is present.

8. The steel strip according to claim 5 , wherein the coating has a composition in which 2.0-2.3 weight % aluminium is present.

9. The steel strip according to claim 1 , wherein the coating has a uniformly distributed (Al+Zn+MgZn2) ternary eutectic structure.

10. The steel strip according to claim 1 , wherein the coating has no Ti, wherein the coating weight of the one-sided coating layer is 37.8 to less than 45 g/m 2 and 2.0-2.3 weight % aluminium is present.

11. The steel strip according to claim 1 , wherein the coating has a composition in which 1.1-1.3 weight % magnesium is present.

12. The steel strip according to claim 1 , wherein in the coating composition 1.2-1.4 weight % magnesium is present.

13. The steel strip according to claim 1 , wherein the steel strip is a carbon steel strip,
wherein in the coating composition 1.2-1.4 weight % magnesium is present and 2.0-2.3 weight % aluminium is present,
wherein the coating weight of the one-sided coating layer is 37.8 to less than 45 g/m 2 .

14. The steel strip according to claim 1 , wherein the coating weight of the one-sided coating layer is 37.8 to 43.6 g/m 2 .

15. The steel strip according to claim 14 , wherein in the coating composition 1.1-1.2 weight % magnesium is present.

16. The steel strip according to claim 1 , wherein the optional total weight of Sn, Bi, Sb, Ln, Ce, Ti, Sc, Sr and/or B is <0.1 weight %.

17. The steel strip according to claim 1 , wherein the coating weight on each side of the metal strip is <37.8 to 43.6 g/m 2 .

18. The steel strip according to claim 1 , wherein Z is in a range from 5 to 8 mm and wherein each said gas knife has a distance above the coating bath of at most 400 mm.

19. A method for providing a Zn—Al—Mg coating on a steel strip of claim 1 using a hot dip coating process with a coating bath, wherein the thickness of the coating is controlled using gas knifes above the coating bath, wherein to obtain a good appearance without a beach defect the coating on the steel strip is given a composition consisting of:
1.2-1.5 weight % magnesium;
between 1.8 and 2.4 weight % aluminium;
optional <0.3 weight % of Sn, Bi, Sb, Ln, Ce, Ti, Sc, Sr and/or B in total;
the remainder consisting of zinc and unavoidable impurities;
wherein the Al and Mg contents satisfy the relationship:
Al (in weight %) >1.28 Mg (in weight %)+0.25 with the proviso that if Al is 2.0 weight % then Mg may be 1.4 weight %,
and wherein Z<0.6 e 0.064CW
wherein Z is the distance between each gas knife and the steel strip in mm, and wherein CW is the weight of the one-sided coating layer in g/m 2 ,

wherein CW 35 to <45 g/m 2 , wherein the gas knifes have a distance above the bath of at most 500 mm.

20. The method according to claim 19 , wherein CW<40 g/m 2 .

21. The method according to claim 1 , wherein the gas knifes have a distance above the bath of at most 250 mm.

22. The method according to claim 1 , wherein the strip has a roughness Ra<1.0 μm before entering the coating bath.

23. The method according to claim 19 , wherein the steel strip is a carbon steel strip.

24. The method according to claim 19 , wherein the coated steel strip has a width between 400 and 2500 mm and a gauge between 0.5 and 5 mm.

25. The method according to claim 19 , wherein the coated steel strip has a length between 400 and 40,000 m.

Assignees

• Tata Steel Ijmuiden Bv

Inventors

• Van Eenennaam Jaap Peter
• Chen Shangping
• Toose Edgar Matthijs

Classifications

• C23C2/16

  using fluids under pressure, e.g. air knives · CPC title

• C23C2/06 Primary

  Zinc or cadmium or alloys based thereon · CPC title

• C22C18/04

  with aluminium as the next major constituent · CPC title

• B32B15/013

  one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium · CPC title

• C23C2/20 Primary

  Strips; Plates · CPC title