# US 12,173,407 B2 · Corrosion protection with Al/Zn-based coatings

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- Number: US 12,173,407 B2
- Document ID: US12173407B2
- Status: Granted
- Kind: B2
- Application number: 18/366,827
- Filed: 2023-08-08
- Published: 2024-03-07
- Granted: 2024-12-24
- Earliest claimed: 2009-03-13
- Assignees: Bluescope Steel Limited
- Applicants: Bluescope Steel Limited
- Inventors: Ross McDowall Smith; Qiyang Liu; Bryan Andrew Shedden; Aaron Kiffer Neufeld; Joe Williams; David James Nolan; Wayne Renshaw
- Web page: https://patentgrep.com/patent/US12173407B2

## CPC

- C23C 2/12: Aluminium or alloys based thereon
- C23C 2/06: Zinc or cadmium or alloys based thereon
- C23C 2/14: Removing excess of molten coatings; Controlling or regulating the coating thickness
- Y10T 428/12021: having composition or density gradient or differential porosity
- Y10T 428/12028: Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, etc.]
- 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)
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

Red rust staining of Al/Zn coated steel strip in “acid rain” or “polluted” environments can be minimised by forming the coating as an Al—Zn—Si—Mg alloy coating with an OT:SDAS ratio greater than a value of 0.5:1, where OT is the overlay thickness on a surface of the strip and SDAS is the measure of the secondary dendrite arm spacing for the Al-rich alpha phase dendrites in the coating. Red rust staining in “acid rain” or “polluted” environments and corrosion at cut edges in marine environments can be minimised in Al—Zn—Si—Mg alloy coatings on steel strip by selection of the composition (principally Mg and Si) and solidification control (principally by cooling rate) and forming Mg2Si phase particles of a particular morphology in interdendritic channels.

## Claims

### Claim 1

A coated metal strip with a corrosion resistant coating of an Al—Zn—Si—Mg alloy on one or both surfaces of the metal strip, wherein the coating comprises
40-65 wt. % Al,
35-50 wt. % Zn,
1-3 wt. % Si,
1.5-2.5 wt. % Mg, and
optionally other elements in amounts of less than 0.5 wt. % for each other element;
the coating having
an overlay thickness greater than 5 μm and less than 30 μm; and
a microstructure comprising
dendrites of Al-rich alpha phase,
interdendritic channels of Zn-rich eutectic phase mixture extending from the metal strip, and
Mg2Si phase particles in greater than 60% of the interdendritic channels, wherein the Mg2Si phase particles in the interdendritic channels block corrosion along the interdendritic channels.

### Claim 2 (depends on 1)

The coated metal strip defined in claim 1 wherein greater than 70% of the total volume fraction of Mg2Si phase in the coating is in the lower two thirds of the overlay thickness of the coating.

### Claim 3 (depends on 1)

The coated metal strip defined in claim 1 wherein the Mg2Si phase particles in the interdendritic channels have a size range and a spacial distribution that activates the Al-rich alpha phase to provide sacrificial protection.

### Claim 4 (depends on 1)

The coated metal strip defined in claim 1 wherein greater than 70% of the interdendritic channels are blocked by Mg2Si phase particles.

### Claim 5 (depends on 1)

The coated metal strip defined in claim 1 wherein the overlay thickness of the coating is less than 20 μm.

### Claim 6 (depends on 1)

The coated metal strip defined in claim 1 wherein the Zn concentration is 39-48 wt. %.

### Claim 7 (depends on 1)

The coated metal strip defined in claim 1 wherein the Mg concentration is 1.7-2.3 wt. %.

### Claim 8 (depends on 1)

The coated metal strip defined in claim 1 wherein the Si concentration is 1.3-2.5 wt. %.

### Claim 9 (depends on 1)

The coated metal strip defined in claim 1 wherein the metal strip is a steel strip.