Microstructural characterization and mechanical properties of a Mg–6Zn–3Sn–2Al alloy

The microstructures and the phases of the Mg–6Zn–3Sn–2Al alloy in the different states were characterized by OM, XRD and TEM. Almost all the MgZn phase was dissolved in the alloy after solutionizing, while part of the Mg2Sn phase was retained. In addition, no visible grain growth was detected. The long rod-like β′1β′1 phase, the hexagonal tablet-like β′2β′2 phase, the lath-like MgZn phase, the coarse particle-like MgZn2 phase and the short rod-like Mg2Sn phase were observed in the as-aged alloy. The Sn addition had no obvious effect on the morphology and crystal structure of the precipitates in the Mg–Zn system. The as-aged alloy exhibited higher strength but lower elongation than the as-cast alloy at ambient temperature and 150 °C. With the increment of temperature, the strength of the alloys in both states decreased, while their elongations increased. Moreover, the former showed a slighter decrease in strength than the latter with the temperature increasing. It can be mainly ascribe to the strengthening of thermally stable β′1β′1 and Mg2Sn precipitates along grain boundaries and within the matrix.