| Magnesium is the lightest commercial construction metals 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 is widely accepted that magnesium alloy is" the green engineering metals of the 21st century". 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 microstructures and properties of AZ31 by upsetting at different temperatures and at different strains will be discussed. The deformation mechanics of AZ31 by upsetting at different temperatures will be found.The material used in this investigation was as-cast AZ31 magnesium alloy. The experiment was divided into two parts according to different forging temperatures. The first part is the test of the cold upsetting. These samples were upsetted to different strain(s2.5%~15%)at room temperature, 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 different temperatures for some hours. The next step was the observation of microstructures and hardness'measurement of the annealing samples. The last step was observation of the fracture and crack expansion.The second part is the test of hot upsetting. Some samples were upsetted to 40% at different temperatures(200℃~500℃) , other samples were upsetted to different strains(7.5%~20%)at 400℃. The microstructures of hot-upsetted samples were observed by OM and TEM, according to which their size of DRX was measured. The compression failure tests were carried out with the samples of strains 40% at different temperatures and then the fracture was observed by SEM.The investigation shows that twinning play an important role in the process of the deformation at room temperature. Much twinning is produced during the process of deformation at room temperature, twin is the mainly deformation manner and the volume friction of twinning increases as the deformation increases. Temperature and strain have an influence on the microstructres of annealed samples. The recrystallization occurs when it reaches the critical strain. Twinning promotes the recrystallization. The twinning is produced more after deformation, the efficiency of refine is better. Compare to no-deforming samples, the mechiancal property of samples promote greatly after anneal. Fracture belongs to brittleness transcrystalline fracture. During the hot-upsetting, at 400℃, when the strain exceeds 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 40%, the DRX grain will be survied until the temperature exceeds 250℃. The volume fraction of DRX grain increases as the temperature rises. The mechanism of dynamic recrystallization (DRX) is based on twinning.
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