Corrosion protection with Al / Zn-based coatings

摘要

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 Si phase particles of a particular morphology in interdendritic channels.