Corrosion resistance of hot dip Zn-Mg galvanized steel sheet

Hot dip Zn-Mg galvanized steel sheet having excellent corrosion resistance was developed aiming to elongate the life time of hot-dip galvanized steel sheet. This pre-coated steel sheet also revealed the customers cost down due to the reduction of post-dip galvanized process. It has excellent corrosion performance in various corrosion tests and atmospheric exposure tests especially improves corrosion resistance in salt damaged area, which are problematic now. And, it has superior sliding abrasion in forming due to the relative high surface hardness. Therefore, this coated steel sheet has a promising future as a environmentally-harmonizing and resource-saving coated steel sheet. The microstructure and corrosion behavior of hot dip Zn-Mg galvanized steel sheet were also investigated by some surface analysis, corrosion tests and electrochemical methods. The corrosion products of Zn-Mg were more compact and stable than that of Zn. For instance, in the case of test environment containing relative high Cl, ZnCl2.4Zn(OH)(2) formed on Zn-Mg coatings was very stable for a long time. Especially, cathodic reaction (oxygen reduction reaction) was restricted according to the polarization curve.