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.