Constitutive Modeling of Slip, Twinning and Detwinning for Mg Alloy and Inhomogeneous Evolution of Microstructure

To investigate the relationship between macro-plastic behavior and meso-deformation mechanism of Mg alloy AZ31, the mathematical models for various deformation mechanisms of slip, twinning and detwinning are established, respectively. Furthermore, in order to capture the Bauschinger effect under cyclic loading, the back stress is introduced into the three independent deformation mechanisms, respectively. Finally, using the above-mentioned model, a new cyclic plastic constitutive model based on the constitutive theory of crystal deformation for magnesium alloy is established. On this basis, the numerical simulation for AZ31 under cyclic loading with the axial strain amplitude of 1.2% is carried out in accordance with the aforementioned crystal plasticity theory associated with the representative volume element model. The comparison between the stress–strain curves obtained from the simulation and the experiments shows that the macroscopic mechanical responses predicted using the proposed model are in good agreement with the experimental results. In particular, the unique characteristics of cyclic macro-plastic behavior observed in the experiments can be satisfactorily captured by the presented crystal plasticity model. At the mesoscale, these features are caused by the alternate occurrence of twinning and detwinning mechanisms. The further analysis of meso-plastic behavior shows that there are heterogeneous distributions of twinning, stress–strain and stress triaxiality in polycrystal under cyclic loading.