The influence of bending mode ultrasonic-assisted friction stir welding of Al-6061-T6 alloy on residual stress, welding force and macrostructure

Residual stress can affect the properties and performance of materials. Since it is an important factor in all welding processes, either fusion welding or friction stir welding, thus, novel complementary methods should be integrated with friction stir welding for reduction of residual stress. In this work, a hybrid method was introduced called bending mode ultrasonic-assisted friction stir welding (BM-UAFSW) and its effect under various vibration amplitudes was investigated on the longitudinal residual stress in a cross-section area of 3 mm and thickness of 5 mm AA6061-T6 plates using contour method. The findings indicated that BM-UAFSW can decrease the maximum longitudinal residual stress by up to 24% in relation with the conventional FSW. In addition, the reaction forces along tool axis and macrostructure observation were provided to illustrate the effect of high-frequency bending mode ultrasonic vibrations on the welding force and welding quality. All the results suggest that BM-UAFSW with amplitude of 2 and 3 mu m provides the best outcome for the welding of 3 and 5 mm thick joints, respectively.