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 (673K) 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 Mg2Ca and Mg2Sn particles, respectively.