Cyclic deformation behavior of friction-stir-welded dissimilar AA5083-to-AA2024 joints: Effect of microstructure and loading history

The microstructural evolution across the friction-stir-welded dissimilar AA5083-H112 to AA2024-T351 aluminum alloy joints was characterized via electron backscatter diffraction (EBSD), aiming to identify the effect of inhomogeneous microstructures on the tensile properties and cyclic deformation behavior along with the influence of loading history. Results show that the top region of the stir zone (SZ) mainly consisted of AA2024 which was initially positioned on the retreating side during welding. On the AA5083 side, the lowest density of the geometrically-necessary dislocations (GNDs) assessed from the local misorientations of 0 degrees-2 degrees appeared in the SZ, while it occurred in the heat-affected zone (HAZ) of the AA2024 side. The fractions of recrystallized grains in the AA5083 SZ and AA2024 SZ were similar to 73% and similar to 34%, respectively. Strain localization and the resultant failure occurred in the lowest hardness zone of the AA5083 side. The extent of cyclic hardening increased as the stress amplitude increased. Both plastic strain amplitude and plastic strain energy density decreased with increasing number of cycles at higher total strain amplitudes. In the stepwise cyclic deformation tests in the form of ascending-descending loading, the prior cyclic deformation process tended to generate more stabilized structure and performance.