Micromechanical modeling of cyclic plastic deformation of ZK60 Mg alloy using 3D full -field crystal plasticity coupled with computational homogenization

A spatially resolved crystal plasticity finite element model in conjunction with computational homogenization is proposed to simulate the micromechanisms of cyclic plastic deformation of an extruded ZK60 magnesium alloy. Dislocation slipping, twinning and detwinning are included through an integrated framework. The ability of the proposed model to reproduce experimental macroscopic responses has been evaluated through the numerical solution of a real representative volume element (RVE) of microstructure under strain-controlled cyclic loading. The proposed model can capture the main macroscopic cyclic plastic characteristics of the ZK60 extruded Mg alloy including asymmetry in stress-strain curve, mechanical anisotropy, strain amplitude dependency of response, mean stress evolution and Bauschinger effect. Simulations were carried out up to 1% macroscopic strain. In agreement with experimental texture, both basal as well as off-basal grains, whose c-axes deviate from being normal to extrusion direction (ED), are included in the RVE. To assess the micromechanisms of cyclic plastic deformation three distinct grain ensembles termed as microtextures have been implanted in the bulk texture. The mixed grain cluster consists of both basal and off-basal grains. Off-basal microtexture is comprised of off basal grains. Twinned microtexture is formed when a few contiguous grains are in a favorable position for twinning. The simulation results show that under certain conditions, off-basal and twinned microtextures can act as a channel for long-range flow softening and strain localization which evolves with loading cycles. Additionally, severe incompatible plastic deformation stemming from the presence of micro-textures induces short or long-range evolving intergranular stress concentration.