<p>This study presents computational and experimental analysis of friction stir welding (FSW) for dissimilar aluminium copper joints using COMSOL Multiphysics. Heat transfer, fluid flow, and material mixing were simulated with the level set module for two tool profiles tapered threaded cylindrical and square pins. Results show that the threaded cylindrical pin provides superior material flow and mixing, while the square pin generates higher torque and excess heat, increasing the risk of defects. Thus, the threaded cylindrical profile is more effective for producing defect-free welds with stable flow and refined microstructure. Microstructural and crystallographic characterization of the stir zone was performed using electron backscatter diffraction (EBSD), pole figures (PF), and orientation distribution functions (ODF). EBSD revealed fine equiaxed grains with a high fraction of high-angle grain boundaries, confirming extensive continuous dynamic recrystallization, along with localized discontinuous dynamic recrystallization near the Al–Cu interface. PF and ODF analyses identified dominant shear texture components together with recrystallization textures such as cube, P, F, and rotating cube. The coexistence of these components highlights the combined influence of severe plastic deformation and thermally driven recrystallization in stabilizing the weld microstructure. Overall, the threaded cylindrical pin is recommended for achieving sound, high-strength dissimilar Al–Cu FSW joints.</p>