Investigation of the Ability of the Corrosion Protection of Zn-Mg Coatings

Presently Zn-Mg coatings are being developed as a contribution to next generation of galvanized steel. However, the underlying corrosion mechanism is still under debate. In this paper we show that Raman spectroscopy next to electrochemical methods (linear sweep voltammetry and electrochemical impedance spectroscopy) can successfully be used to help in identifying the corrosion products of Zn-Mg coated galvanized steel (ZMS) when dipped into 3 wt. % NaCl aqueous solution at ambient temperature (25 °C). The obtained results are compared to galvanized steel. This study reveals that in the case of ZMS, Mg is mainly anodically dissolved forming a compact layer of Mg(OH)₂/MgO and MgCO₃. It is believed that the formation of this compact layer and the insulating properties of MgO, due to its large band gap, are responsible for the increased corrosion resistance of the alloy.