A Foundation Study Of Superplasticity Of Magnesium Alloy

Magnesium alloy has hexagonal close-packed (HCP) structure,very limted slips and poor plastic deformation ability. Superplasticity is an important method to improve plasticity of magnesium alloy. In this paper, some basic issues on the superplastic deformation process of AZ31 magnesium alloy was investigated.Instability is a common phenomenon in the superplastic tensile deformation, superplastic tensile instability and the general instability are significantly different. According to the geometric instability criterion ,the critical stress of geometric instability was deduced under the conditions of superplastic tensile with constant strain rate; The effect of temperature and strain rate on load instability and the geometric instability of AZ31 magnesium alloy was experimental studied on the superplastic tensile. The results show that: critical strain of load instability as well as the geometric instability increase with temperature or strain rate decreases, the critical strain of geometric instability is greater than that of load instability. Superplastic tensile load Instability that does not appear immediately with geometric instability, but after going through a uniform deformation then the geometric instability began to emerge.Strain rate sensitivity exponent m is an important indicator of superplasticity and is general obtained through the experiments. By studying the changes of sections, a parameters K was putted forward to characterize the contractions of cross-section after superplastic tensile , and the relations of K with the material parameters and deformation parameters were established to measure superplasticity of materials. Cavitation is a structure in the process of superplastic deformation ,it has an important influence to superplasticity of the material, so the number of cavitation measurement is meaningful. Based on the hypothesis that work-hardening and the softening of recrystallization was in dynamic equilibrium when superplastic tensile, this paper presents a new method to measure cavitation exponent based on the material tensile curve.