ALUMINIUM, ZINC, SILICON, MAGNESIUM ALLOY METAL COATED STEEL STRIP WITH VARIATION IN COATING THICKNESS CONTROLLED TO REDUCE Mg2Si IN THE SURFACE

摘要

586488 A hot-dip coating method is disclosed for forming a coating of a corrosion-resistant Al-Zn-Si-Mg alloy on a steel strip. The method is characterised by passing the steel strip through a hot dip coating bath that contains aluminium, zinc, silicon, magnesium and optionally other elements to form an alloy coating on the strip. The thickness of the coating varies by no more than 40% in any given 5 mm diameter section of the coating. Limiting the coating thickness variation allows diffusion away from the surface of Mg and Si so that there is no more than 10% by weight of Mg2Si particles in the surface of the coating. This reduces mottling a mottling defect on the surface of the coating.