Role of icosahedral phase in enhancing the strength of Mg–Sn–Zn–Al alloy

The effect of the selection of the secondary solidification phase on the mechanical properties of the Mg–Sn–Zn and Mg–Sn–Zn–Al alloy rolled sheets has been investigated in the present study. The as-cast microstructure of Mg–7Sn–2Zn (in wt.%) alloy consists of α-Mg dendrite and interdendritic Mg2Sn and MgZn2 phases, while that of Mg–7Sn–5Zn–2Al alloy consists of α-Mg dendrite and interdendritic Mg2Sn and icosahedral (I-) phases. The micron scale interdendritic I-phase in the as-cast Mg–7Sn–5Zn–2Al alloy dissolves into the matrix during homogenizing treatment, and appears again in the α-Mg matrix as 0.1–0.5 μm size fine spherical precipitates after rolling process. As a result, the Mg–7Sn–5Zn–2Al alloy exhibits high yield strength of 318 MPa in as-rolled state. The high level of strength is attributed to the presence of finely distributed Mg2Sn and I-phase particles embedded in the α-Mg matrix.

► Quasicrystalline phase leads to enhancement of the strength of Mg-based alloys.
► In as-cast Mg–Sn–Zn alloy interdendritic Mg2Sn and MgZn2 phases are present.
► Addition of Al in ternary alloy forms icosahedral phase in the interdendritic region.
► The rolled Mg–Sn–Zn–Al sheet exhibits higher level of strength than ternary alloy.