Automobile manufacturers are interested in lightweight materials, including magnesium, to increase vehicle fuel economy, improve performance and reduce emissions. In this work the deformation behavior of as-cast and rolled magnesium AZ31 alloy has been studied. In as-cast material, it was found that reheating at 400°C and above for 60 minutes increased the homogeneity of the as-cast structure and gave rise to repeatable deformation. At compression temperatures above 300°C dynamic recrystallization occurred; below 200°C, there was significant twinning. Annealing completely recrystallized the structure deformed below 200°C, but did not change the dynamically recrystallized structure. AZ31 alloy was also rolled at temperatures of 350, 400 and 450°C and rolling speeds of 20 and 50 rpm for 15 and 30% reduction in thickness to produce sheet. Before rolling, the alloy was preheated for I and 10 hours at the rolling temperatures. The sheets were then tensile tested at 300, 400 and 450°C with strain rates of 0.1, 0.01 and 0.001s-1. The flow curves and microstructures indicated that the tensile deformation mechanism changed with processing conditions. Two deformation mechanisms were present in the magnesium sheet depending on the strain rate and grain size. At slow strain rates and small grain size, the active deformation mechanism was grain boundary sliding. As grain sizes increased there was also a component of dislocation creep. At the fast strain rate, the deformation mechanism, regardless of grain size, was dislocation creep. At a true strain rate of 0.001s-1, it was found that rolling at 350°C with 30% reduction per pass yielded the finest microstructure and subsequently, the best hot deformation characteristics. At a true strain rate of 0.1s-1, rolling at 450°C with 30% reduction per pass yielded a coarser, more recrystallized microstructure with best hot deformation characteristics.
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