Synergistically double-sided FSW with dual-tool interaction

Synergistically double-sided friction stir welding (SDS-FSW) has the potential to mitigate through-thickness thermo-mechanical non-uniformity in medium-thickness aluminum joints, yet its linkage between process and property remains insufficiently understood. Here, SDS-FSW of 6061-T6 aluminum alloy is investigated via coupled thermo-mechanical simulation and experiments, with conventional sequentially double-sided FSW (CDS-FSW) as a benchmark. SDS-FSW converts two sequential asymmetric thermal cycles into a single intensified cycle and increases mid-thickness mixing, producing defect-free joints. The SDS-FSW joint achieves an ultimate tensile strength of 240 MPa, a yield strength of 159 MPa and an elongation of 5.2%, while reducing welding deformation by more than 55% relative to CDS-FSW. The results demonstrate that SDS-FSW is an effective route to improve joint homogeneity and mechanical properties in aluminum alloys.