Effect of Grain Size and Volume Fraction of Eutectic Structure on Mechanical Properties and Corrosion Behavior of As-Cast Zn–Mg Binary Alloys

In this work, the effects of Mg content on the microstructure evolution, mechanical properties, and corrosion behavior of as-cast Zn-xMg (x = 0.1, 0.3, 0.5, 1.0, 1.5, and 3.0, wt.%) binary alloys were investigated. The microstructure of as-cast alloys is composed of α-Zn matrix and a ternary eutectic phase (α-Zn + Mg2Zn11+MgZn2). With the increase of Mg content, the average grain size of the alloys decreases from 104 μm to 11 μm while the volume fraction of eutectic structure increases from 3% to 84%, resulting in the improvement of tensile strength. In vitro immersion tests demonstrate that the corrosion rate decreases to a minimum value of 0.086 mm y−1 as Mg content increases from 0.1 to 0.3, followed by an increasing trend with the further increase of Mg content. The variation of corrosion rate with Mg content originates from the competition between the positive effect of grain refinement and the negative effective of eutectic volume fraction increment. Zn-0.3 Mg alloy has the optimal corrosion resistance because of the dominant role of grain refinement induced corrosion resistance enhancement. In addition, the corrosion mechanism varies from localized pitting to a more uniform corrosion as Mg content rises.