Negative lateral strain ratio induced by deformation twinning in magnesium alloy AZ31

We show that any highly textured metal that deforms predominantly by deformation twinning can exhibit a negative lateral strain ratio under uni-axial loading. Theoretical calculations of lateral strains caused by tension twinning on the { 1   0   1 ¯   2 } plane in a magnesium single crystal predicts this behavior, and we verify this by direct measurements of lateral strains in highly textured commercial magnesium alloy AZ31 deformed in uniaxial compression. The R values of AZ31 plate compressed in the rolling direction at −100 °C and 25 °C show negative values at compressive strain up to ∼0.03, and increase with strain and temperature. These evolution trends of R value are found be closely related to activity of { 1   0   1 ¯   2 } twinning. This approach is extended to compression twinning in zinc, for which theoretical calculations show the same effect on lateral strain ratio.