Crystal plasticity modeling of the multiaxial ratchetting of extruded AZ31 Mg alloy

Abstract

Macroscopic experimental observations on the non-proportional multiaxial ratchetting of extruded AZ31 Mg alloy is firstly summarized, and corresponding microscopic investigations are conducted by electron backscatter diffraction (EBSD) technology on the Mg alloy before and after the multiaxial ratchetting. Then, a constitutive model was developed in the framework of crystal plasticity for the Mg alloy single crystal at finite strain. Various plastic deformation mechanisms including twinning, detwinning and dislocation glide are considered. Meanwhile, three different kinematic hardening laws are presented to capture the evolutions of back stresses associated with different deformation mechanisms, respectively, from the macroscopic and microscopic experimental results. Also, the residual twins generated in the cyclic deformation and their accumulations are considered. The developed single crystal model is extended to the polycrystalline version by means of a newly developed elasto-viscoplastic self-consistent homogenization scheme at finite strain. Finally, the non-proportional multiaxial ratchetting of the AZ31 Mg alloy is reproduced by the developed model. Conclusions can be drawn that the developed model can effectively describe the multiaxial ratchetting and its dependences on the stress level and stress path as well as the relative texture evolution during the multiaxial ratchetting of the AZ31 Mg alloy.