A study on corrosion behaviour of magnetron sputtered Zn-Mg coating deposited onto electro-galvanized steel

In this study, a nano-structured Zn-Mg coating was prepared by magnetron co-sputtering on electro-galvanized carbon steel. The microstructure and phase structure of Zn-Mg coating and its behaviour during saltwater immersion test were investigated by means of optical microscopy (OM), environmental scanning electron microscopy (ESEM), X-ray diffractometry (XRD) and electrochemical workstation. Electrochemical impedance spectroscopy (EIS) as a sensitive and reliable method was employed in corrosion mechanism research. The results show the formation process of a passive film on the surface of Zn-Mg coating during the immersion time range. The formation mechanism of this dense corrosion product Zn5(OH)8Cl2·H2O layer was also discussed. An electroplated Zn coating was also investigated for comparison purposes.