Microstructure and mechanical properties of rheo-diecasting AZ91D Mg alloy

Taking AZ91D magnesium alloy as experimental material, the rheo-diecasting process was implemented by combining the self-developed taper barrel rheomoulding(TBR) machine with high pressure die casting(HPDC) machine. Microstructural characteristics of the rheo-diecasting components were investigated in different processing parameters. Microstructural evolution and solidification behavior of the semisolid slurry during the rheo-diecasting process were discussed, and tensile properties of the components were studied as well. The results show that, with the rotation speed of the internal taper barrel increasing, the microstructure of the components becomes fine with solid particles nearly spherical and uniformly distributed on the matrix. When the rotation speed is 700 r/min, the primary α-Mg particles have an average size of about 45 μm and a shape factor of about 0.81; the primary α-Mg particles become round and homogeneous with shearing temperature increasing, but the average size is slightly larger. The solidification of the alloy melt during the rheo-diecasting process is composed of two distinct stages: the primary solidification and the secondary solidification. Compared with the conventional die-casting process, the rheo-diecasting process would improve the tensile properties of the components, especially the elongation by 80%.