Mechanical anisotropy improvement in ultrafine-grained ZK61 magnesium alloy rods fabricated by cyclic extrusion and compression

摘要

Nearly un-textured ZK61 Mg alloy rods with ultrafine-grain structure were successfully fabricated by cyclic extrusion and compression. Microstructure uniformity and mechanical anisotropy were strikingly improved by grain refinement and texture randomization during the processing. Tension/compression asymmetry displayed significant dependence on texture, essentially attributed to {10-12} twinning. With the processing, tensions showed an increased tendency of twinning deformation, but the majority were still dominated by multi-slip mechanism and exhibited higher yield strengths related to pyramidal ((c+a)) slip. Comparatively, compressions showed a decreased tendency of twinning and commonly exhibited lower yield strengths determined by the stress to activate {10-12} twinning. The twining-induced deformation is initially dominated by twinning, but gradually becoming by slips especially after twinning is exhausted. It can conclude that any measurement that suppresses twinning activity in both tension and compression is beneficial to improving both tension/compression strength and asymmetry.