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.