Bluescope Steel Limited

Nippon Steel Corporation

Nippon Steel Coated Sheet Corporation

Wayne Andrew Renshaw

Qiyang Liu

Joe Williams

Aaron Kiffer Neufeld

Ross McDowall Smith

David James Nolan

Bryan Andrew Shedden

Geoff Tapsell

Nobuyuki Shimoda

Shiro Fujii

Cat Tu

Nega Setargew

Michael Angel Lopez

Jason Hodges

Shuichi Kondo

Takashi Hirasawa

Ross Mcdowall Smith

Andrew Vincent Micallef

Paul Donaldson

An Al—Zn—Si—Mg alloy coated strip that has MgSi particles in the coating microstructure is disclosed. The distribution of MgSi particles is such that the surface of the coating has only a small proportion of MgSi particles or is at least substantially free of any MgSi particles.

Metal-coated steel strip

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 MgSi phase particles of a particular morphology in interdendritic channels.

Corrosion protection with Al/Zn-based coatings

An Al&#x2014;Zn&#x2014;Si&#x2014;Mg alloy coated strip that has MgSi particles in the coating microstructure is disclosed. The distribution of MgSi particles is such that the surface of the coating has only a small proportion of MgSi particles or is at least substantially free of any MgSi particles.

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&#x2014;Zn&#x2014;Si&#x2014;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 &#x201c;acid rain&#x201d; or &#x201c;polluted&#x201d; environments and corrosion at cut edges in marine environments can be minimised in Al&#x2014;Zn&#x2014;Si&#x2014;Mg alloy coatings on steel strip by selection of the composition (principally Mg and Si) and solidification control (principally by cooling rate) and forming MgSi phase particles of a particular morphology in interdendritic channels.

A method of forming a coating of an Al&#x2014;Zn&#x2014;Si&#x2014;Mg alloy on a steel strip to form an Al&#x2014;Zn&#x2014;Mg&#x2014;Si coated steel strip is disclosed. The method includes the steps of dipping steel strip into a bath of molten Al&#x2014;Zn&#x2014;Si&#x2014;Mg alloy and forming a coating of the alloy on exposed surfaces of the steel strip and cooling the coated strip with cooling water. The cooling step includes controlling the p H of cooling water to be in a range of pH 5-9. Particular embodiments focus on Al&#x2014;Zn&#x2014;Si&#x2014;Mg alloys that contain the following elements in % by weight: Zn: 2 to 19, Si: 0.01 to 2, Mg: 1 to 10, and Balance Al and unavoidable impurities.

Method of producing metal-coated steel strip

A method of forming an Al&#x2014;Zn&#x2014;Si&#x2014;Mg alloy coating on a steel strip includes dipping steel strip into a bath of molten Al&#x2014;Zn&#x2014;Si&#x2014;Mg alloy and forming a coating of the alloy on exposed surfaces of the steel strip. The method also includes controlling conditions in the molten coating bath and downstream of the coating bath so that there is a uniform Al/Zn ratio across the surface of the coating formed on the steel strip. An Al&#x2014;Zn&#x2014;Mg&#x2014;Si coated steel strip includes a uniform Al/Zn ratio on the surface or the outermost 1-2 &#x3bc;m of the Al&#x2014;Zn&#x2014;Si&#x2014;Mg alloy coating.

A method of forming a coating of an Al&#x2014;Zn&#x2014;Si&#x2014;Mg alloy on a steel strip to form an Al&#x2014;Zn&#x2014;Mg&#x2014;Si coated steel strip is disclosed. The method includes the steps of dipping steel strip into a bath of molten Al&#x2014;Zn&#x2014;Si&#x2014;Mg alloy and forming a coating of the alloy on exposed surfaces of the steel strip and cooling the coated strip with cooling water. The cooling step includes controlling the pH of cooling water to be in a range of p H 5-9. Particular embodiments focus on Al&#x2014;Zn&#x2014;Si&#x2014;Mg alloys that contain the following elements in % by weight: Zn: 30 to 60, Si: 0.3 to 3, Mg: 0.3 to 10, and Balance Al and unavoidable impurities.

A method of controlling 'rough coating' and 'pinhole-uncoated' surface defects on a steel strip coated with a aluminum-zinc-silicon alloy. The alloy has 50-60% wt Al, 37-46% wt Zn and 1.2-2.3% wt Si. The method includes heat treating the steel strip in a heat treatment furnace and thereafter hot-dip coating the strip in a molten bath and thereby forming a coating of the alloy on the steel strip. The method is characterized by controlling the concentration of (i) strontium or (ii) calcium or (iii) strontium and calcium in the molten bath to be at least 2 ppm.

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Unanderra, Australia

Wayne Andrew Renshaw