Microstructure Evolution and Mechanical Properties of Medical Material Mg-3Zn Alloy Prepared by Semi-solid Powder Injection Moulding

Medical Mg-based alloys are extensively applied because of its degradability, low elastic modulus, etc. In this study, Mg-3Zn alloy was prepared by semisolid powder injection moulding, a novel method combining metal injection moulding and thixomoulding in one step. Firstly, pure Mg powders with 3 wt% of pure Zn powders (the mean diameter is 50 mu m) were mixed, and then the mixture were injected at 540, 560, 580, 600, and 620 degrees C, respectively with the loading force of 5 t. The effect of injection temperature on the microstructure, and its corresponding mechanical properties were investigated. The densification process and combination mechanism were analyzed as well. The results show that as the temperature increases, relative density, the compressive strength and microhardness increase first and then decrease when the temperature reaches to 620 degrees C. The highest relative density, microhardness and compressive strength is 97.4%, 125 HV, 315.4MPa, respectively at the injection temperature of 600 degrees C. The microstructure is mainly composed of alpha-Mg and intermetallic phases (MgZn2, Mg4Zn7 and Mg51Zn20), the grain morphology is equiaxed grains with size of about similar to 30 mu m. When injected at low temperature, the main combination mechanism of powders is hot rolling densification. When injected at high temperature, flowing and filling of liquid is the main combination mechanism. Broken-up of particles and deformation including viscoplastic deformation contributes to the densification. More Mg was dissolved into Zn as the temperature increases, and the liquid fraction is mainly influenced by the dissolved Mg content.