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 o C 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.
The microstructure and age hardening response of deformed Mg-1.5Mn-xSn (x = 1 and 5, wt.%) alloys under three different aging temperatures (100°C, 150°C, 200°C) have been investigated. The aging behavior and the mechanical properties are improved by increasing Sn content. On ther other hand, the pre-rolling process is an effective method to improve the age hardening response, and therefore the mechanical properties of ERA (extruded + rolled + aging treatment) state alloys are improved compared with those of EA (extrusion + aging treatment) state samples. The improved mechanical properties of ERA alloys are mainly related to the extensive twins and dislocations formed during the extrusion/rolling processes and Mg2Sn precipitates formed in the aging treatment.
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