Corrosion protection with Al/Zn-based coatings

Patent metadata

Field	Value
Publication number	US-12173407-B2
Application number	US-202318366827-A
Country	US
Kind code	B2
Filing date	Aug 8, 2023
Priority date	Mar 13, 2009
Publication date	Dec 24, 2024
Grant date	Dec 24, 2024

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 Mg 2 Si phase particles of a particular morphology in interdendritic channels.

First claim

What is claimed is:

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
Mg 2 Si phase particles in greater than 60% of the interdendritic channels, wherein the Mg 2 Si phase particles in the interdendritic channels block corrosion along the interdendritic channels.

2. The coated metal strip defined in claim 1 wherein greater than 70% of the total volume fraction of Mg 2 Si phase in the coating is in the lower two thirds of the overlay thickness of the coating.

3. The coated metal strip defined in claim 1 wherein the Mg 2 Si 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.

4. The coated metal strip defined in claim 1 wherein greater than 70% of the interdendritic channels are blocked by Mg 2 Si phase particles.

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

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

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

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

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

Assignees

• Bluescope Steel Ltd

Inventors

• Smith Ross Mcdowall
• Liu Qiyang
• Shedden Bryan Andrew
• Neufeld Aaron Kiffer
• Williams Joe
• Nolan David James
• Renshaw Wayne

Classifications

• C23C2/14

  Removing excess of molten coatings; Controlling or regulating the coating thickness · CPC title

• C23C2/06 Primary

  Zinc or cadmium or alloys based thereon · CPC title

• Y10T428/12028

  Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, etc.] · CPC title

• Y10T428/12021

  having composition or density gradient or differential porosity · CPC title

• C23C2/40

  Plates; Strips · CPC title