Role of secondary phase in microstructural stability of as-extruded Mg–Sn–Ca at high temperature

The microstructural stability in three as-extruded Mg alloys (Mg–0.6Ca, Mg–1.9Sn and Mg–1.9Sn–0.6Ca) at high temperature (673 K) is studied by optical microscope (OM), scanning electron microscopy (SEM), and its effect on the mechanical properties is tested by tensile test. The grain size of Mg–1.9Sn–0.6Ca alloy is retained at high temperature, while grains in Mg–0.6Ca grow at some degree and in Mg–1.9Sn they coarsen seriously. Additionally, the tensile strength of Mg–1.9Sn–0.6Ca is also most thermally stable. The outstanding microstructural and mechanical stability of as-extruded Mg–1.9Sn–0.6Ca alloy is attributed to the strong pinning effect of stable CaMgSn secondary phase. The poor performances of Mg–0.6Ca and Mg–1.9Sn are due to the dissolution of Mg 2 Ca and Mg 2 Sn particles, respectively.