Evidence for exceptional low temperature ductility in polycrystalline magnesium processed by severe plastic deformation

An investigation was conducted to examine the mechanical behavior and microstructure evolution during deformation of ultrafine-grained pure magnesium at low temperatures within the temperature range of 296-373 K. Discs were processed by high-pressure torsion until saturation in grain refinement. Dynamic hardness testing revealed a gradual increase in strain rate sensitivity up to m approximate to 0.2. High ductility was observed in the ultrafine-grained magnesium including an exceptional elongation of similar to 360% in tension at room temperature and stable deformation in micropillar compression. Grain coarsening and an increase in frequency of grain boundaries with misorientations in the range 15 degrees-45 degrees occurred during deformation in tension. The experimental evidence, when combined with an analysis of the deformation behavior, suggests that grain boundary sliding plays a key role in low strain rate deformation of pure magnesium when the grain sizes are at and below similar to 5 mu m. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.