Parameter study on BT-FSW welds in 8 mm-thick AA7050-T7451

This study aimed to evaluate the welding parameters of the Bobbin Tool Friction Stir Welding (BT-FSW) process applied to an 8 mm thick AA7050 T7451 aluminum alloy. The research focused on obtaining welds with good visual quality, a low rate of macrostructural defects compared to the base material, and a welding speed equal to or greater than 3 mm/s. The study included Vickers microhardness tests, visual inspections, temperature measurements on the tool shoulders, and macrographic analysis of the welded joints. The results indicated that the welding speed and tool rotation speed directly affect burr formation, the occurrence of internal defects, and the process temperature, highlighting the importance of precise control of these parameters for obtaining high-quality welds. An initial incidence of a large number of defects was observed in the mechanical mixing region of the weld. These defects were reduced by maintaining the tool feed rate at 3 mm/s, reducing the initial tool shoulder gap from 7.86 to 7.8 mm, and adequately controlling the tool rotation speed. The best experimental values were obtained for the condition with a feed rate of 3 mm/s, a gap of 7.8 mm, and a tool/weld entry speed of 500/200 RPM, with a low incidence of volumetric voids and a microhardness of 64% of the base material value at the critical point.