The effect of hardening laws and thermal softening on modeling residual stresses in FSW of aluminum alloy 2024-T3

In the present paper, a numerical model consisting of a heat transfer analysis based on the Thermal Pseudo Mechanical (TPM) model for heat generation, and a sequentially coupled quasi-static stress analysis with a built-in metallurgical softening model was implemented in ABAQUS. Both isotropic and kinematic rules of hardening were used in order to study the effect of the hardening law on the residual stresses as well as on the final yield stress. This numerical model was then applied in two different cases. Firstly, a very simple 1D Satoh test was modeled. Different combinations of either isotropic or kinematic hardening together with the metallurgical softening model were applied in order to give a first impression of the tendencies in residual stresses in friction stir welds when choosing different hardening and softening behaviors. Secondly, real friction stir butt welding of aluminum alloy 2024-T3 were simulated and compared with experimentally obtained results for both temperatures and residual stresses (using the slitting method). The comparisons showed good agreement regarding temperatures whereas the residual stress comparisons indicated different sensitivities for the cold and hot welding conditions toward the choice of hardening rules and especially whether including the softening model or not