Implications of twinning on the microstructure development, crystallographic texture and mechanical performance of Mg alloys- a critical review

Deformation twinning is profusely activated in the Mg alloys due to lower critical resolved shear stress (CRSS) compared to the non-basal slip systems (prismatic <a> and pyramidal <c + a>) and plays a significant role in texture reorientation, grain refinement and enhancement of mechanical performance. Twinning is a sequential process comprising twin nucleation, twin propagation and twin growth, hence several intrinsic and extrinsic parameters that facilitate or suppress the process have been critically reviewed. The dependence of twinning on the grain size, deformation temperature, favorable grain orientation and shear strain have been thoroughly discussed in the context of published literature and an attempt has been made to provide a benchmark conclusive finding based on the majority of works. Furthermore, the subsequent effect of twinning on the mechanical performance of Mg alloys, including ductility, formability and tension-compression asymmetry has been discussed in detail. Lastly, the stability of twins, including stress and thermal stability, is summarized and critical issues related to pertinent bottlenecks have been addressed.