| The tasks of this research are,1), preparative of AZ91D magnesium alloy billets by pouring them using low superheat process; 2), reheating the billets into semi-solid state; and 3), forming a component of kickstand of generator of the type of JH70 motorcycle in semi-solid die casting processing.The experience was conducted using cooling slope and low superheat processes, effects of pouring temperature and the degree of slope on the billet's structure were researched. The results show that, 1) the fined grains can be achieved when the pouring temperature is 650℃ and the degree of slope is 45°in the process of cooling slope, 2)the structures of billets poured using low superheat at 595℃ consist of agglometrate-likeδcrystals and few eutectics phase. Although the grains are a bit coarser than that using cooling slope, the low superheat process was adopted because of the simply equipment and process through the comparison of the structure character of the primary billets and the processing character using the two processes each other.With a high-frequency induced heating equipment and a device for temperature measuring in lab, reasonable semi-solid process parameters, such as an appropriate semi-solid remelting temperature, and heating power and speed, of AZ91D magnesium alloy in the process of the high-frequency reheating, effects of these parameters on thixotropic behaviors of billets, and the evolvement of structure in the process of reheating were researched. The results show that, 1) proper semi-solid remelting temperatures of the alloy is in the range of 580℃～583℃; 2) in the condition of optimized reheating processing, the temperature deviation in a billet is 0℃～1℃, and the thixotropy of billet is good; 3) agglometrate-likeδcrystals in original billet changed into rosette-like and rotundity-like δgrains after reheating, which may meet the need of semi-solid thixoforming; 4) Solute diffusion plays an important role in the course of remelting billet. Firstly, liquid phase occurs on eutectic boundaries with low melting point in the structure, Secondly, the melting point of the concave parts of the irregular solid grains decreases and the irregular solid grains are refined by fusing off them at the concaved locations owing to curvature mechanism. At the last stage of remelting, the shape factor of δ grains increases a little owing to the mechanism of interface tension between liquid and isolated grains.The component was successfully formed in practice in semi-solid die casting processing by the semi-solid processing parameters obtained in laboratory at the locale of the factory of Chongqing JiuFang casting limited liability Company of JiaLing Group. In the processing of the semi-soliddie casting, appropriate semi-solid casting parameters and the sizes of ingate area were investigated .The results shows that, in the process of semi-solid die casting, the size of ingate is bigger and the thickness is almost equal to the thickness of component's wall. The optimized parameters of thixoforming of the component are 580℃ to 583℃ for remelting billets, 280℃ to 300℃ for mould temperature, 4.5 m/s for speed of pierce of the machine, 75 MPa for extrusion pressure, and, 350 MPa for maintenance pressure. Thus a casting with good structure and perfect appearance can be attained.The structures of billet and casting were observed, and the percentages ofδgrains, the average diameters of δ grains and the shape factor ofδgrains were measured using a quantificational metallographic analysis system. The gathering liquid area in remelt billets vanished after extrusion and the liquid phase and solid phase have been mixed each other in casting. Because the velocity of liquid phase is higher than that of solid phase during extrusion, the solid fraction in the location of piercer is 75％,65% in the ingate, 57％ in the casting near ingate and 55% in the location far away from ingate. The size of solid crystals minish a little because of shear mechanism. The mean diameter of δ crystals in the billet is about 160u...
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