An X-ray diffraction study of the influence of linear and changing strain paths on strain and texture evolution in AA6111-T4 aluminium alloy sheets

Multi-stage automotive stamping processes involve both linear and changing strain paths. While extensive research exists on linear strain paths and discontinuous strain path change, the study of continuous strain path change is limited due to the need for sophisticated experimental procedures. In this paper, the effect of continuous strain path change on strain, strain hardening behaviour, microstructure, and texture evolution was compared with that of discontinuous strain path change in AA6111-T4 aluminium alloy using a novel experimental setup comprising an in-situ mechanical rig and cruciform sample. An X-ray source was used to obtain diffraction patterns, which were analysed to measure diffraction intensities and lattice strains at the {111}, {200}, {220} and {311} lattice planes to study strain hardening behaviour, microstructure, and texture evolution during the loading paths. The experiments were repeated outside the X-ray diffraction chamber to study macroscopic strain evolution and hardening behaviour of the samples using a digital image correlation system. It was found that the absence of unloading and reloading in the continuous strain path change posed challenges for plastic deformation in the next deformation stage, leading to strain softening, premature failure, and relatively weaker textural development. Conversely, the presence of unloading and reloading in the discontinuous strain path change facilitated increased plastic deformation in the next deformation stage, resulting in strain hardening, delayed failure, and stronger textural development.