Plastic incompatibility stresses arising from slip and twinning in extruded AZ31 magnesium alloy: In-situ synchrotron diffraction analysis using self-consistent modeling

Abstract

This study presents a comprehensive investigation into the bulk internal stress evolution within an extruded AZ31 magnesium alloy subjected to both in-situ uniaxial tensile and compressive loading. Using energy-dispersive synchrotron X-ray diffraction (ED XRD), first-order macroscopic stresses and second-order plastic incompatibility stresses were successfully quantified in a strongly textured hexagonal close packed (hcp) polycrystalline material. To decouple these stress components from lattice strain determined in many directions and using different reflections, an advanced q -parameter methodology combined with an elastoplastic self-consistent (EPSC) model was applied to the tensile and compressive tests. This methodology was implemented for the first time under compressive conditions involving intensive twinning. The applied approach demonstrates high sensitivity to the sequential activation of slip and twinning systems, revealing that basal slip initiates early second-order plastic incompatibility stresses. The results highlight a distinct deformation asymmetry, characterized by a slip dominated intergranular stress accumulation during tensile loading and a significant twinning induced stress relaxation during compression. By grouping slip systems with equivalent micromechanical impacts, the number of deformation parameters was reduced while maintaining a high quality agreement between model and experiment across nearly 150 measured lattice strains. The developed methodology allows for capturing texture dependent stress partitioning in the material, as well as identifying active plastic deformation mechanisms and determining their direct impact on the overall deformation process. Furthermore, it provides a rigorous framework for validating crystallographic parameters and the grain interaction scheme used in the theoretical model.