Deformation characteristics at room temperature under biaxial tensile stress in textured AZ31 Mg alloy sheets

Tensile and stretch-forming tests were conducted at room temperature on rolled AZ31 Mg alloy sheets with different grain sizes, and deformation behavior under biaxial tensile stress was investigated from the viewpoint of the effects of grain size with the aim of improving stretch formability. The elongation to failure at room temperature increased with decreasing grain size; in contrast, stretch formability increased with increasing grain size. Because the (0 0 0 2) basal planes were intensively distributed parallel to the RD–TD plane in the rolled Mg alloy, the lattice rotation by the twins (such as {101¯1} twin) played a critical role in deformation under biaxial tensile stress, inducing strain in the thickness direction. This resulted in the grain size dependence of stretch formability because the twin formation was enhanced by grain coarsening.