High-speed friction stir butt welding of 25.4 mm thick 7175-T79 aluminum alloy

•First experimental demonstration of high-speed (>500 mm/min) friction stir welding of thick aluminum plates (>10 mm).•High-speed double-sided FSW possesses yield strength improved by 20–24% over slow- to medium-speed one-sided FSW for a 25 mm thick AA7175 plate.•The joint efficiency of as-welded, double-sided high-speed FSW was about 76%.•Significant grain refinement (grain size 1.3 ± 0.8 μm) was evident at the junction of double-sided friction stir welding (FSW). This study presents the first experimental demonstration of high-speed friction stir butt welding of 25.4 mm thick AA7175-T79 aluminum alloy. The utilization of friction stir welding (FSW) tool pin threads that terminate away from the shoulder region reduced stress concentration during tool traversing. This tool design enabled a welding speed above 500 mm/min and a penetration depth greater than 10 mm without pin fracture near the shoulder. Two types of welds were performed: one-sided with full penetration and double-sided with partial penetration of the plate thickness. The junction of the double-sided friction stir welding (FSW) exhibited significant grain refinement (grain size 1.3 ± 0.8 μm) compared to other regions. Cross-weld tensile testing revealed high local strains at the double-sided FSW junction, which improved the yield strength by 20–24% compared to slower one-sided FSW. The joint efficiency of the as-welded, high-speed double-sided FSW was approximately 76% of the base material's ultimate tensile strength.