Magnesium and magnesium alloy are being increasingly used as functional and structural components in the automobile and electronic
industries due to their low density, high strength/stiffness to weight ratio and electromagnetic interference shielding capabilities, good damping capacity, etc. It is desirable to used semi-solid processing technology to produce components free of gas hole and porosity which usually found in those produced by the method of die casting. In this paper, in order to study the deformation behavior of AZ91D magnesium alloy in semi-solid state and obtain the constitutive relationship necessary for numerical simulation, the compression tests are carried out systematically on the Gleeble-1500 material thermo-simulation machine. The temperature' s range of test is 510℃-570℃ and strain rate' s range is 0.1~20s-1. Based on the theory of rigid-viscoplastic finite element and experiment data, the
constitutive equation (σ=AεBT+c·eeeeeeeDT+E·eF/T+Gεt) has been established by regression method. The commercial software DEFORM-3D is employed to simulate the process of
thixoforming a practical automobile wheel of minimized size. Thus the flow and stress-strain field of thixoforming process have been set up and the relationship among stress, strain rate and temperature has been also analyzed. The above works will lay a foundation for magnesium components to improve quality and further practical used in future industry.