Experimental and numerical investigation of cold formability in dissimilar friction stir butt-welded AA5754-H111 and AA6082-T6 sheets

Friction Stir Welding (FSW) enables solid-state joining of dissimilar aluminum sheets for lightweight applications. However, despite extensive studies on tensile and hardness properties, the post-weld cold formability of dissimilar thin-sheet joints and its quantitative correlation with numerical predictions remain scarcely explored. This study uniquely addresses this gap by investigating the cold formability of AA5754-H111/AA6082-T6 butt joints (2 mm) produced under three heat-input levels, obtained by varying travel speed at a fixed rotational rate of 1350 rpm. The joints were characterized through optical microscopy, microhardness mapping, and Erichsen cupping tests (ISO 20482) performed in both intrados and extrados orientations. A simplified approach to the modelling of welded joints, based on Belytschko–Tsai shell elements and literature forming-limit diagrams, was developed to represent weld-zone softening and account for heat-input-dependent variations in softened-zone width. Results show pronounced weld-zone softening in AA6082 relative to AA5754, with an average Erichsen index of about 4 mm across all conditions. Numerical predictions reproduced the experimental values within 2–3% for medium and hot conditions, while slightly underestimating cold conditions. Overall, travel-speed-induced heat input had a limited effect on global biaxial formability, whereas weld soundness (e.g., tunnel defects) influenced local fracture initiation. The combined experimental–numerical framework supports the selection of FSW process windows for dissimilar AA5754/AA6082 tailor-welded blanks, while the proposed numerical approach, thanks to its simplicity, shows potential for application in industrial contexts.