Stress concentration in cryogenic deformed AA2219 friction stir welding joints: experiments and crystal plasticity modeling

: Aluminum alloy 2219 friction stir welding (FSW) joints for rocket propellant tanks are subjected to cryogenic tensile loading, under which microstructural heterogeneity in the welded region can promote local deformation incompatibility and stress concentration, thereby threatening structural reliability. To clarify the grain-scale deformation behavior and stress concentration evolution of AA2219 FSW joints at 77 K, an electron backscatter diffraction (EBSD)-informed crystal plasticity finite element model incorporating the effect of initial residual stress was established. The developed model was validated by the cryogenic tensile stress-strain response. Using the validated model, the grain-scale deformation, grain boundary accommodation, stress concentration evolution, and the role of initial residual stress in AA2219 FSW joints during uniaxial tension were analyzed. It was found that grain orientation heterogeneity was the primary origin of intergranular deformation incompatibility and stress concentration, whereas grain rotation provided only limited accommodation. Grain boundary deformation increased with tensile strain and further enhanced local heterogeneity. Stress localization progressively intensified during deformation and preferentially developed near grain boundaries with large orientation mismatches. In addition, initial residual stress mainly promoted local plastic activation at the early deformation stage, while its influence gradually weakened with further straining. This study provides microstructure-based insight into cryogenic deformation and stress concentration in AA2219 FSW joints.