Thermomechanical couplings of twinning Magnesium over a reversed load path

This study explores the thermomechanical couplings in rolled Magnesium AZ31 under a non-monotonic load path, by first straining in the sense that incites profuse twinning and then reversing the load (to the sense that impedes twinning). The evolution of temperature, stress, and strain during the corresponding compression-tension cycle is measured by in situ infrared thermography combined with digital image correlation. At an intermediate point in the tensile segment, an idiosyncratic thermoelastic effect (normally reserved only for the initial elastic stages of loading in materials) is observed, coincident with the transition between detwinning and slip plasticity. Energy balance analysis reveals that the ratio of the dissipated portion to the total plastic power (Taylor-Quinney coefficient) is significantly lower during twin-dominated deformation (about 0.3) compared to slip plasticity (about 0.6). During detwinning, the coefficient attains a nominal value of 0.5. These findings provide new multiphysics insights into the complex deformation of magnesium, offering a new avenue to refine high-fidelity material models.