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THE WE43 magnesium alloy containing yttrium and mischmetal, which belongs to one of the heat-resistant magnesium alloys, has been recognized as a promising material in the ordnance industry because of the remarkable increase in light weight demands. However, the low strength at room temperature and poor wear resistance of the WE43 magnesium alloy hinder its commercial applications to some extent. To conquer these challenges, it is advisable to develop a WE43 magnesium alloy reinforced by micron-sized ceramic SiC particles. Nevertheless, the application of SiCp/ WE43 is still counteracted by some problems: in particular, turbulent filling of the die results in air entrapment and shrinkage of porosity, and the high forming temperature leads to a decrease in tool life. Thixoextrusion is a thixoforming process where a billet in the semi-solid state is extruded into the desired shape through a cavity die.[1] In comparison with conventional forging, thixoforming needs much less forming loads, so it can produce near-net-shaped components with a complex geometry, which cannot be achieved by forging.[2] On the other hand, in comparison with conventional casting, semi-solid magnesium matrix composites QIANG CHEN, XIANGSHENG XIA and YANG WU are with Southwest Technology and Engineering Research Institute, Chongqing, 400039, P. R. China. GANG CHEN and FEI HAN are with the School of Materials Science and Engineering, Harbin Institute of Technology at Weihai, Weihai, 264209, P. R. China. Contact e-mail: [email protected] Manuscript submitted December 11, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A

exhibit higher viscosity, so macroscopic turbulence can be avoided during die filling, and subsequently, casting defects caused by air entrapment can also be reduced.[3] Although many works have focused on the thixoforming of aluminum alloys and steels, few works have reported on the thixoforming of magnesium matrix composites. Nadal et al.[4] studied the mechanical properties of thixoformed hypoeutectic gray cast iron by thixoforming components at different temperatures and heat-treatment holding times. Salleh et al.[5] studied the microstructural evolution and mechanical properties of thixoformed A319 alloys containing variable amounts of magnesium. They found the Mg element can refine the eutectic silicon and improve the tensile strength. Meng et al.[6] found that a larger pre-deformation, rapid reheating, and shorter holding time were beneficial for refining the microstructures and improving the mechanical properties of Cr-V-Mo steel. Zhang et al.[7] found that the mold temperature had significant effect on the secondary solidification behavior and mechanical properties of thixoforged Mg2Sip/ AM60B in situ composites. Wang et al.[8] developed a visco-plastic constitutive modeling for thixoforming of AA6061 in semi-solid state. Meng et al.[9] proposed a multistage compression method in thixoforging A6061 aluminum alloy and found that it was useful for improving the homogeneity of microstructures and mechanical properties. He