Microstructure, mechanical properties and first-principle analysis of vacuum die-cast Mg–7Al alloy with Sn addition

The influences of Sn element and heat treatment on the microstructure and mechanical properties of Mg–7Al alloy prepared by vacuum die cast (VDC) were studied. The results indicate that α-Mg dendrite and Mg 17 Al 12 are refined and new Mg 2 Sn phase is formed in Mg–7Al alloy with 2 wt% Sn addition. The ultimate tensile strength ( σ b ) of Mg–7Al alloy increases from 205 to 258 MPa (i.e., a 25 % increase). The mechanical properties of Mg–7Al–2Sn (AT72) alloy are further improved through heat treatment because of the dense microstructures processed by VDC. In particular, the mechanical properties of AT72 alloy are greatly improved after solution treatment at 400 °C for 20 h due to solution strengthening of Al and Sn elements and precipitation strengthening of Mg 2 Sn phases. The precipitation strengthening effect of particle Mg 2 Sn phases is more apparent due to the decomposition of Mg 17 Al 12 phases. In addition, from the view of microscopic theory, the effect of Sn on mechanical properties of Mg–7Al alloy was discussed by first-principle calculation.