Sustainable joint integrity in Al 8006/Al 7475 friction stir welding enabled by a hexagonal pin tool

This study explores the friction stir welding (FSW) of dissimilar aluminium alloys, Al 7475 and Al 8006, using a hexagonal pin-profile tool. The study concentrates on fine-tuning three major friction stir welding parameters: tool rotational speed, welding speed and tool tilt angle. Their influence on key mechanical properties, including tensile strength, elongation and Brinell hardness, is examined in detail. An L16 Taguchi orthogonal array is used to structure the experiments and guide the optimization of the butt joints. The single-objective analysis shows that the best combination for achieving the highest tensile strength is 1200 RPM, 60 mm/min and a 2.5° tilt angle. The model’s adjusted R² value of 0.9651 indicates strong predictive reliability. When multiple properties are optimized together, the refined settings (1200 RPM, 50 mm/min and a 2.5° tilt angle) lead to a tensile strength of 390 MPa, elongation of 13% and hardness of 125.5 HB. SEM fracture analysis highlights clear differences in weld morphology. Joints produced at 800–1000 RPM contain deep voids and irregular dimples, while welds made at 1200–1400 RPM show more consistent deformation marked by evenly spread tear ridges and dimples. This research aligns with SDG 9 (Industry, Innovation and Infrastructure) by advancing an efficient solid-state joining route for high-performance lightweight structures, and SDG 12 (Responsible Consumption and Production) through reduced energy use, elimination of filler materials, and minimized process waste in friction stir welding. • Hexagonal pin tool enhances material flow in Al 8006/Al 7475 FSW joints • Optimized FSW parameters achieved tensile strength up to 390 MPa • Taguchi L16 design enabled reliable multi-response optimization • SEM fracture analysis reveals defect-free weld morphology at higher RPM • Sustainable solid-state joining supports lightweight industrial structures