Tension–Compression Yield Asymmetry Influenced by the Variable Deformation Modes in Gradient Structure Mg Alloys

Surface mechanical attrition treatment (SMAT) was carried out on hot-rolled AZ31 Mg samples along two orthogonal directions; as a result, two types of gradient structures with different grain sizes and texture components in different layers were produced. The tension–compression yield asymmetry (YA) was studied using samples with different thicknesses, in order to elucidate the effect of combinations of variable deformation modes operating in different layers of the two oriented SMAT samples. The 0° oriented SMAT sample containing layers with strong basal texture displayed significant YA, because of either dislocation slip or extension twinning domination during tension or compression. By contrast, the 90° oriented SMAT sample containing layers with coexisting orthogonal texture components had an obviously weakened YA, which was attributed to the multi-deformation modes cooperating during tension or compression, i.e., extension twinning or detwinning in conjunction with dislocation slips, leading to close yield stresses compared between tension and compression.