A sub-superplastic forming means that the initial stage of the part forming is controlled by the dislocation creep and no grain boundary sliding because of the coarse grain of the blank material. The dynamic recrystallization appeared during the initial stage of the forming may cause grain refinement, so the deform mechanism may change from dislocation creep to grain boundary sliding, then the superplastic forming will appear if the conditions of the fine grain and proper temperature are satisfied in the following stage of the forming process. Here a forming process of a magnesium alloy part, as a sub-superplastic forming, is simulated numerically. Of cause, the simulated results include grain size variety, deformation mechanism change and strain rate sensitivity index m value increase. Finally the experiment is presented for validation of simulated results. The key of the numerical simulation is to develop a material model which includes both superplastic model and the hot plastic model considering dynamic recrystallization.
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