Effects of heat treatment on microstructure and microhardness of Mg-3Sn-1Y alloy

A nominal composition of Mg-3Sn-1Y (mass fraction, %) magnesium alloy was prepared by casting with flux protection in electric-resistance furnace. The microstructures as-cast, solution treatment and aging hardening of the Mg-3Sn-1Y alloy by different aging treatments after solution treatment were investigated by an Olympus GX71 optical microscope (OM), an FEI QUANTA 400 scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectroscop (EDS), a RigakuD/max-3C X-ray diffraction (XRD), a TUKON2100 Vickers hardness tester and a CRY-2P differential thermal analyzer (DTA). The results show that as-cast Mg-3Sn-1Y alloy consists of dendritic α-Mg and intermittent mesh inter-dendrite boundaries Mg₂Sn phase, the dispersion tiny particles and fine rod-shaped MgSnY phase. After the solution treatment, the Mg₂Sn phase is completely redissolved, and the MgSnY phase with the high temperature stability still distributes in the matrix. The addition of yttrium elements can improve the high temperature stability of Mg-Sn alloy. Mg-3Sn-1Y alloy exhibits obvious aging hardening characteristics. The increase of the aging temperature is advantageous to the occurrence of aging hardening peak to some extent. On the contrary, grain growth of the matrix will decrease the function of separation and strengthening and delay the appearance of aging hardening peak as the ageing temperature is too high.