Microstructure and Mechanical Properties of Extruded Mg-Sm-Ca Alloys

Microstructure, age hardening response and mechanical properties of Mg-4.0Sm-xCa (x=0.5, 1.0, 1.5, wt%) alloys extruded followed by isothermal aging at 200 oC were investigated. The results indicate that with the addition of Ca, the bulk and particle-like Mg41Sm5 phase containing Ca and the needle/rod-like Mg2Ca phase are formed in the Mg matrix, grains of the alloy are refined and tensile mechanical properties are improved remarkably. Under T5 (peak-aging) condition, the Mg-4.0Sm-1.0Ca alloy shows the smallest grain size of 5.1 μm. With the increase of Ca content the amount of Mg2Ca phase increases gradually, but that of the bulk Ca-containing Mg41Sm5 phase, which is mainly distributed at the grain boundaries, decreases obviously when Ca content reaches 1.5 wt%. The peak-aged Mg-4.0Sm-1.0Ca alloy exhibits the highest hardness HV (820 MPa) and the optimal ultimate tensile strength, yield tensile strength and elongation of 267 MPa, 189 MPa and 24%, respectively. The improved mechanical properties of the alloy are attributed to the grain refinement, the solution strengthening and the precipitation strengthening of Mg2Ca phase and Mg41Sm5 phase.