# US 11,306,382 B2 · Method for providing a Zn—Al—Mg coating, and such coating

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- Number: US 11,306,382 B2
- Document ID: US11306382B2
- Status: Granted
- Kind: B2
- Application number: 16/318,229
- Filed: 2017-07-20
- Published: 2019-08-01
- Granted: 2022-04-19
- Earliest claimed: 2016-07-20
- Assignees: Tata Steel Ijmuiden B.V.
- Applicants: Tata Steel Ijmuiden B.V.
- Inventors: Jaap Peter Van Eenennaam; Shangping Chen; Edgar Matthijs Toose
- Web page: https://patentgrep.com/patent/US11306382B2

## CPC

- C23C 2/20: Strips; Plates
- B32B 15/013: {one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium}
- C22C 18/04: with aluminium as the next major constituent
- C23C 2/06: Zinc or cadmium or alloys based thereon
- C23C 2/16: using fluids under pressure, e.g. air knives
- C23C 2/40: Plates; Strips
- C23C: COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL (making metal-coated products by extrusion B21C23/22; covering with metal by connecting pre-existing layers to articles, see the relevant places, e.g. B21D39/00, B23K; metallising of glass C03C; metallising mortars, concrete, artificial stone, ceramics or natural stone C04B41/00; enamelling of, or applying a vitreous layer to, metals C23D; treating metal surfaces or coating of metals by electrolysis or electrophoresis C25D; single-crystal film growth C30B; by metallising textiles D06M11/83; decorating textiles by locally metallising D06Q1/04)
- B32B: LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- C22C: ALLOYS (treatment of alloys C21D, C22F)

## 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.

## Claims

### Claim 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/m2, and
wherein the coating does not contain binary (Zn+MgZn2) 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 e0.064CW, 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/m2 and wherein each said gas knife has a distance above the coating bath of at most 500 mm.

### Claim 2 (depends on 1)

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/m2 and no surface defects are present at all.

### Claim 3 (depends on 2)

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.

### Claim 4 (depends on 2)

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.

### Claim 5 (depends on 1)

The steel strip according to claim 1, wherein the coating weight on each side of the metal strip 35 to less than 40 g/m2, 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.

### Claim 6 (depends on 1)

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

### Claim 7 (depends on 2)

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

### Claim 8 (depends on 5)

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

### Claim 9 (depends on 1)

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

### Claim 10 (depends on 1)

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/m2 and 2.0-2.3 weight % aluminium is present.

### Claim 11 (depends on 1)

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

### Claim 12 (depends on 1)

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

### Claim 13 (depends on 1)

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/m2.

### Claim 14 (depends on 1)

The steel strip according to claim 1, wherein the coating weight of the one-sided coating layer is 37.8 to 43.6 g/m2.

### Claim 15 (depends on 14)

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

### Claim 16 (depends on 1)

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 %.

### Claim 17 (depends on 1)

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/m2.

### Claim 18 (depends on 1)

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.

### Claim 19 (depends on 1)

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 e0.064CW
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/m2,
wherein CW 35 to <45 g/m2, wherein the gas knifes have a distance above the bath of at most 500 mm.

### Claim 20 (depends on 19)

The method according to claim 19, wherein CW<40 g/m2.

### Claim 21 (depends on 1)

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

### Claim 22 (depends on 1)

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

### Claim 23 (depends on 19)

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

### Claim 24 (depends on 19)

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.

### Claim 25 (depends on 19)

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