Effect of Sn addition on the microstructure and mechanical properties of Mg–6Zn–1Mn (wt.%) alloy

•Sn addition can improve the mechanical properties of the extruded Mg–Zn–Mn alloy.•T6 treatments can markedly improve the strengths of the extruded Mg–Zn–Mn–Sn alloys.•Mg–6Zn–1Mn–4Sn alloy with double aging treatment exhibits the highest strengths.•High strength is attributed to combined precipitation strengthening of β1′ and Mg2Sn.

The microstructure and mechanical properties of Mg–6Zn–1Mn alloys with varying Sn contents (0, 1, 2, 4, 6, 8 and 10 wt.%) have been examined using optical microscopy (OM), X-ray diffractometer (XRD), scanning electron microscopy(SEM), transmission electron microscopy (TEM), hardness test and uniaxial tensile test at room temperature, respectively. The samples were prepared by hot-extrusion after casting. The results showed that the as-cast Sn-containing alloys consisted of α-Mg, Mg7Zn3, Mn and Mg2Sn phases. T6 treatments could obviously improve the strengths of the as-extruded samples, and the double aged samples exhibited enhanced age-hardening response at an earlier stage compared to the single aged ones. Among them, the 4 wt.% Sn containing sample with double peak aging after solution treatment had the highest strengths and moderate elongation. Microstructure characterization indicated that the high-strengths of the peak aged alloys were mainly determined by a synergistic effect on precipitation strengthening of β1′ (MgZn2) and Mg2Sn precipitates, and the precipitates after double aging were finer than those after single aging.