| Popis: |
The effects of Ca addition on the microstructure and mechanical properties of Mg–Zn–Sn–Mn alloys were investigated in this study. The Mg–6Zn–4Sn–1Mn–xCa (x = 0, 0.2, 0.5, 1 and 2 wt%) alloys consist of the α-Mg, Mg2Sn, Mg7Zn3, MgZn, α-Mn, CaMgSn, MgZn2, Mg2Ca and Ca2Mg6Zn3 phases. With increasing Ca content, the eutectic phase and grains were refined, and the morphologies of the CaMgSn phases changed from point-like to needle-like, rod-like and lath-like. At room temperature, small amounts of Ca can improve properties owing to refinement strengthening. The two-stage aged Mg–6Zn–4Sn–1Mn–0.2Ca alloy has the best comprehensive properties at room temperature, with an ultimate tensile strength (UTS), yield strength (YS) and elongation of 407 MPa, 392 MPa and 6.2%, respectively. When the Ca content increased, the number of CaMgSn phases increased, and the morphologies coarsened. Further, it was a brittle phase, resulting in the deterioration of alloy properties. At high temperatures, a small amount of Ca can improve the high-temperature plasticity. The elongations of the as-extruded Mg–6Zn–4Sn–1Mn–0.2Ca alloy were 76.9% (150 °C) and 133.8% (200 °C). A high Ca concentration can significantly improve the high-temperature strengths because of the good thermal stability of the CaMgSn phases, the best UTS and YS are 160 MPa and 136 MPa, respectively, in as-extruded Mg–6Zn–4Sn–1Mn–2Ca alloy at 150 °C. |
