Cyclic hardening behavior and deformation mechanisms of friction-stir-welded dissimilar AA5083-to-AA2024 joints with heterogeneous microstructures

The aim of this study was to elucidate cyclic hardening behavior and deformation mechanisms of the strain-hardened zones of friction-stir-welded (FSWed) dissimilar AA5083-to-AA2024 aluminum alloy joints (with a heterogeneous microstructure) after cyclic deformation via quaasi-in-situ electron backscatter diffraction (EBSD) technique and transmission electron microscopy (TEM) examinations. The extent of cyclic hardening was observed to decrease with increasing number of cycles at a constant total strain amplitude. Strain localization occurred mainly in the stir zone (SZ) and heat-affected zone (HAZ) on the AA5083 side, accompanied by an increasing density of dislocations during cyclic deformation identified via both EBSD and TEM. The strain hardening capacity of AA5083 SZ was significantly higher than that of AA5083 HAZ based on the density of geometrically-necessary dislocations (GNDs). The {111}-oriented grains exhibited a higher strain hardening capacity than other grains. Cracks initiated and propagated in the AA5083 HAZ along with the presence of shear bands. The evolution of GNDs played a predominant role in the AA5083 SZ, while the evolution of statistically-stored dislocations (SSDs) was dominant in the AA5083 HAZ during cyclic deformation.