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The evolution of microstructure in a Mg 3.4%AI-0.16%Zn-0.33%Mn alloy tube was studied during deformation by ring hoop tension testing (RHTT). When the tests were carried out at moderate temperatures and relatively high strain rates, the accompanying c-axis strains were mainly accommodated by twin formation. At temperatures above 200°C and the lowest strain rate (0.001s-1), the formation of voids in the partially dynamically recrystallized regions caused premature fracture. The microstructural development in hot gasformed samples was similar to that observed during RHTT testing. These results indicate that RHTT testing is an effective way of studying the deformation behavior of Mg alloys during tube gas forming.

The deformation characteristics of a commercial AZ31 magnesium sheet alloy were investigated at elevated temperatures. Tensile experiments were conducted at temperatures 300°C, 400°C and 450°C and at strain rates, 0.001s-1, 0.01s-1 and 0.1s-1. Depending on the test temperature, fracture analysis of failed specimens revealed three different types of failure: (1) by moderate necking, (2) by interlinkage cavity, (3) by strong necking. Plastic strain ratios, r-values were derived from the strain ratios of width and thickness of the fractured tensile specimens. The r-value increased with increasing temperature and strain rate.

Understanding the role of the slip systems and their evolution with temperature is critical to the correct simulation of the mechanical behavior of magnesium alloys. In this paper, relations are proposed for evolution of the CRSS values of different slip systems and strain-rate sensitivity factor, stating them as functions of temperature and strain-rate. These relations are used in conjunction with the Crystal Plasticity Finite Element (CPFE) model for prediction of stress-strain curves and r-values at elevated temperatures (75°C to 250°C). The new relations can predict the decrease in stress level, the anisotropy of the material, and the decrease in the difference between the r-values in the RD and the TD with the increase in temperature. The results confirm the trends predicted with Taylor-type and VPSC models. In particular, they confirm the high activity of the slip systems at higher temperatures.