An experimental study of the mechanical behavior of rolled AZ31B magnesium alloy under combined axial-torsion loading

Abstract

The mechanical behavior and microstructure at fracture of a rolled AZ31B magnesium alloy were experimentally investigated using tubular specimens subjected to combined axial-torsion loading with different ratios of the axial and shear stress components. The stress state influences the stress-strain responses. The equivalent stress-equivalent plastic strain curves under tension-torsion loading show a sigmoidal shape and the peak value of the equivalent strain hardening rate increases as the ratio of the axial stress to the shear stress increases. Under compression-torsion, the equivalent stress-equivalent plastic strain curves show a concave-down shape, and the equivalent strain hardening rate decreases at faster rates as the ratio of the axial stress to the shear stress increases. Among all the loading conditions investigated, pure tension and pure compression result in the highest strength, and torsion combined with a slight tension has the lowest strength. The trend of ductility is inversely proportional to the strength with respect to the influence of the combined axial-torsion loading. Detailed twinning structures reveal that extensive tension twins are induced under tension-torsion loading paths. Conversely, a combination of tension and compression twins is observed under compression-torsion loading due to the high Schmid factors of the compression twins resulted from the grains with favorable orientations. The significant effect of the stress state on the post-fracture texture is explained in terms of the twin variant favorability which is dominated by the crystal orientation relative to the orientation of the applied principal stresses. The experimental results are critical for the development and validation of constitutive models for magnesium alloys under multiaxial loading.