Effects of Mg on microstructure and corrosion properties of Zn–Mg alloy

•Zn–Mg alloys with different Mg contents were prepared by melting-casting method.•The microhardness of Zn–Mg alloy increased with increasing Mg content.•EIS test shows that the impedance of Zn–3 wt.% Mg alloy is higher than that of Zn.•Zn–3 wt.% Mg alloy has nano-structure and possesses the best corrosion property.•The nano-structure of Zn–3 wt.% Mg alloy contributes to a general corrosion.

Zn–Mg cast alloys with different Mg contents were prepared. Their microstructures, chemical compositions, microhardness and corrosion resistances were investigated in details, and compared with pure Zn. The alloy containing 3 wt.% Mg showed nano-structure and possessed the best corrosion resistance. Electrochemical tests in 3.5 wt.% NaCl solution indicated that the corrosion potential of Zn–3 wt.% Mg alloy is more positive than that of Zn, and the corrosion current density is about 34% the value of pure Zn. The results of EIS tests were simulated to investigate the mechanism of this improvement. The corrosion rate decreased when the Mg content is higher than 3 wt.%, which is likely related to the formation of the hexagonal Mg rich structure. The microhardness of Zn–Mg alloy increased with increasing Mg content, and is likely attributed to the formation of more Zn–Mg intermetallics.