Twinning-induced anomaly in the yield surface of highly textured Mg–3Al–1Zn plate

The evolution of stress and lateral strains with applied strain was determined by uniaxial loading in the principal directions of a highly textured Mg–3Al–1Zn plate. The material exhibits negative lateral strain ratios when twinning dominates deformation. This leads to a yield surface with a distinct shape, with a high curvature under a balanced biaxial stress state and a shift in plane-strain compression conditions from the third to the second and fourth quadrants of the yield surface.

Research highlights
► We examine the texture effects on lateral strains of AZ31 alloys.
► Calculation of strain field caused by twinning suggests a negative R-value.
► In-plane compression test of AZ31 proves the negative R-value.
► Extensive twinning leads to an anomalous yield surface.