# US 12,180,594 B2 · Metal-coated steel strip > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,180,594 B2 - Document ID: US12180594B2 - Status: Granted - Kind: B2 - Application number: 18/488,673 - Filed: 2023-10-17 - Published: 2024-04-11 - Granted: 2024-12-31 - Earliest claimed: 2008-03-13 - Assignees: Bluescope Steel Limited - Applicants: Bluescope Steel Limited - Inventors: Qiyang Liu; Wayne Renshaw; Joe Williams - Web page: https://patentgrep.com/patent/US12180594B2 ## CPC - C23C 2/06: Zinc or cadmium or alloys based thereon - C23C 2/14: Removing excess of molten coatings; Controlling or regulating the coating thickness - C23C 2/29: {Cooling or quenching} - C23C 30/00: Coating with metallic material characterised only by the composition of the metallic material, i.e. not characterised by the coating process (C23C26/00, C23C28/00 take precedence) - Y10T 428/12757: Fe - Y10T 428/12972: Containing 0.01-1.7% carbon [i.e., steel] - Y10T 428/12979: Containing more than 10% nonferrous elements [e.g., high alloy, stainless] - 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 An Al—Zn—Si—Mg alloy coated strip that has Mg2Si particles in the coating microstructure is disclosed. The distribution of Mg2Si particles is such that the surface of the coating has only a small proportion of Mg2Si particles or is at least substantially free of any Mg2Si particles. ## Claims ### Claim 1 A hot-dip coating method to reduce mottling defect on a surface of an alloy coating of a coated steel strip, the method comprising: passing a steel strip through a hot dip coating bath that contains aluminium, zinc, silicon, and magnesium to form an alloy coating on the steel strip, wherein the alloy coating comprises, in weight %, 40% to 60% aluminium; 40% to 60% zinc; 0.3% to 3% silicon; and 0.3% to 10% magnesium, and controlling a short range coating thickness variation of the alloy coating to be no more than 40% in a 5 mm diameter section of the coating; controlling solidification of the alloy coating, including: cooling the coated steel strip at a cooling rate of: greater than 11° C./sec and less than 80° C./sec for coating masses up to 75 grams per square meter of strip surface per side, or greater than 11° C./sec and less than 50° C./sec for coating masses of 75-100 grams per square meter of strip surface per side, wherein the alloy coating has a microstructure comprising Mg2Si particles, and wherein the method controls the distribution of the Mg2Si within the coating microstructure such that the surface of the alloy coating has no more than 10 wt % of Mg2Si particles to thereby reduce mottling defect on the surface of the alloy coating. ### Claim 2 (depends on 1) The method according to claim 1, wherein the coating thickness variation is no more than 30% in a 5 mm diameter section of the coating. ### Claim 3 (depends on 1) The method according to claim 1, further comprising controlling a coating thickness of the alloy coating to be greater than 7 μm and less than 30 μm. ### Claim 4 (depends on 3) The method according to claim 3, wherein, for a coating thickness of 22 μm, the maximum thickness in a region of the coating greater than 1 mm in diameter is 27 μm. ### Claim 5 (depends on 1) The method according to claim 1, wherein the alloy coating comprises 55 wt % aluminium. ### Claim 6 (depends on 1) The method according to claim 1, wherein the alloy coating comprises 1.5 wt % silicon. ### Claim 7 (depends on 1) The method according to claim 1, wherein the alloy coating comprises 2.0 wt % magnesium. ### Claim 8 (depends on 1) The method according to claim 1, wherein the alloy coating comprises no strontium. ### Claim 9 (depends on 1) The method according to claim 1, wherein the hot dip coating bath comprises one or more of strontium, iron, vanadium, and chromium and the alloy coating comprises one or more of strontium, iron, vanadium, and chromium. ### Claim 10 (depends on 9) The method according to claim 9, wherein the hot dip coating bath comprises 250 ppm to 3000 ppm strontium. ### Claim 11 (depends on 9) The method according to claim 9, wherein the hot dip coating bath comprises less than 3000 ppm strontium. ### Claim 12 (depends on 9) The method according to claim 9, wherein the alloy coating comprises more than 250 ppm strontium. ### Claim 13 (depends on 9) The method according to claim 9, wherein the alloy coating comprises more than 500 ppm strontium. ### Claim 14 (depends on 9) The method according to claim 9, wherein the alloy coating comprises more than 1000 ppm strontium. ### Claim 15 (depends on 9) The method according to claim 9, wherein the alloy coating comprises less than 3000 ppm strontium. ### Claim 16 (depends on 1) The method according to claim 1, wherein the surface of the alloy coating comprises no Mg2Si particles. ### Claim 17 (depends on 1) The method according to claim 1, wherein the surface of the alloy coating is substantially free of Mg2Si particles. ### Claim 18 (depends on 1) The method according to claim 1, wherein the coated steel strip is passed through a coating thickness control station to control the coating thickness. ### Claim 19 (depends on 1) The method according to claim 1, wherein the coating thickness control station is a gas knife or gas wiping station.