| Magnesium is the lightest commercial construction metals being used in practice at present. At the same time, magnesium alloys have lower density, the highest strength to weigh ratio, good thermal conductivity , electrical conductivity, damping capacity, and good electromagnetic interference shielding property, the property of being easy to manufacture and recyclable, therefore it has been used several years in the fields of aerspace, astronautic instruments, automobile, computer, electricity , communication and household appliances. But magnesium alloy has a hexagonal close-packed (hcp) crystal structure with limited number of operative slip systems at room temperature, so magnesium alloys are normally low formability near the room temperature, and limits the expansion of magnesium alloy applications. However, up to date the research of wrought magnesium alloys mainly focused on the extrusion and rolling. Little information about the instantaneous deformation behavior and the mechanical properties of AZ31 magnesium alloys after forging is avaible. In this paper, the deformation mechanics of AZ31 by upsetting at different temperatures will be discussed. The method of improving the mechanical property of magnesium alloys will be found by the investigation of anneal after room deformation.The material used in this investigation was as-cast AZ31 magnesium alloy. The experiment was divide into two parts according to different forging temperatures. The first part is the test of the cold upsetting. These samples were upsetted to different strains(2.5%～15%)at room temperature, and their microstructures were observed by optical microsope and TEM. Simultaneously the as-cast and cold-upsetting samples were analysed by XRD. Successionally, A series of annealing experiments were made with different strains'samples at various temperatures for different times. The next step is the observation of microstructures and hardness'measurement of the annealing samples, so that the influence rules of microstructures and properties will be achieved with annealing temperatures, annealing times and different strains. The compression failure tests were carried out at constant strain rate of 0.3 s ?1 with the samples of strains10%.The second part is the test of hot upsetting. Some samples were upsetted to 15% at different temperatures(180℃～500℃) , other samples were upsetted to different strains(7.5%～20%)at 400℃. The microstructures of hot-upsetted samples were observed by OM, according to which measure their size of DRX. The compression failure tests were carried out at constant strain rate of 0.3 s ?1 with the samples of strains15% at different temperatures.The investigation shows that twinning play an important role in the process of deformation at room temperature. Many twinnings are produced during the process of deformation at room temperature, twinning deformation is the mainly deformation manner, and the volume friction of twin increases as the deformation increases. Time, temperature and strain have an influence on the microstructres of annealed samples. When the temperature increase, the velocity of recrystallization rises. A large amount of recrystal grain reveals at the boundary of origin grain and twins. After anneal, the work-hardenging was released and the size of grain was obviously refined. The twin are produced more after deformation, the efficiency of refine is better. Compare to as-cast samples, the mechiancal property of samples promote greatly after anneal. During the hot-upsetting, at 400℃, when the strain exceed 7.5%, the DRX grain will be observed. With the increase of strain, the volume fraction of DRX grain gets more. When the strain is 15% , the DRX grain will be survied until the temperature exceed 350℃. The volume fraction of DRX grain increase as the temperature rise. The mechanisms of dynamic recrystallization (DRX) is based on twinning.
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