Microstructural Evolution and Mechanical Properties of As-Cast Mg-12Zn Alloys with Different Al Additions

In this study, Mg-12Zn magnesium alloys alloyed with Al additions (0, 2, 4, 6, 8 and 10, wt.%) were fabricated by permanent mould casting. The Al content on their microstructure and mechanical properties were systematically examined with an optical microscope (OM), a scanning electron microscope (SEM), an X-ray diffractometer (XRD) and mechanical tests at room temperature. The experimental results indicate that the microstructure of the alloys is mainly composed of α-Mg and semi-continuous or continuous eutectic phases. A higher addition of Al (≥6%) causes the generation of the Mg17Al12 phases. Notably, the grain sizes of the alloys gradually decrease, whilst the partial morphology of some eutectic phases is modified into lamellar structure with increasing of Al addition. Mechanical properties characterization manifested that, the alloys with different Al additions reveal distinguishing tensile properties. Among them, the alloy with 4% Al provides an excellent mechanical properties, i.e., a UTS of 206 MPa and an EL of 7.92%, which is respectively higher 28 MPa and 1.08% than that of ZA120 alloy. The deterioration in the tensile properties for the higher Al-bearing alloys is possibly related to the lamellar structure, coarse and continuous net-work morphology and β-Mg17Al12 phases, respectively.