A three-dimensional mechanistic study of the drivers of classical twin nucleation and variant selection in Mg alloys: A mesoscale modelling and experimental study

Abstract

This work presents a detailed investigation of twin inception to identify site of twinning, variant type selected, and the strain to nucleate it within a full 3D reconstructed microstructure obtained using 3D-EBSD. Microstructurally-faithful 3D crystal plasticity analysis provides quantitative insight to show that stored energy density is a key factor (rather than stress or other criteria) which identifies the experimentally observed twin nucleation site (which supersedes twin inception), and the strain necessary to drive nucleation. 3D (as opposed to 2D surface) analysis has been shown to be essential. The critical energy density for twin nucleation was found to be ∼0.015 Jm-2 in Mg alloy AZ31. Further, at the predicted nucleation site, the experimentally observed twin variant is shown to be driven by the local twin resolved shear stress.