This study investigates the plastic deformation mechanisms of AZ31 magnesium alloy using in-situ neutron diffraction and Crystallite Group Method (CGM). In-situ neutron diffraction enables measurement of the stress tensor for specific grain families within a policrystal by determining lattice strains from diffraction peaks associated with the same grain family, observed from multiple orientations and hkl reflections. Tracking the evolution of the stress tensor makes it possible to experimentally determine the Critical Resolved Shear Stresses (CRSS) and to characterise the hardening behaviour of different slip and twinning systems.
Tensile tests were performed along the rolling direction (RD), while compression tests were conducted along the normal direction (ND), and at 30° (ND30) to the ND, allowing assessment of the anisotropic mechanical response. The CGM allowed direct determination of grain-level stresses for preferred crystallographic orientations, leading to unambiguous CRSS values and, notably, an improved estimate for the basal slip system from the ND30 test, compared to previous findings [1]. These experimentally derived CRSS values, along with the evolution of Resolved Shear Stresses (RSS), were used to validate and calibrate the Elastic-Plastic Self-Consistent (EPSC) model adapted for hexagonal crystal structures. The combined experimental-modelling approach enhances understanding of plastic anisotropy in AZ31 alloy and improves the predictive capability of the EPSC framework for magnesium alloys subjected to complex loading conditions.