Evolution of residual stress field in 6N01 aluminum alloy friction stir welding joint

Based on the characteristics of friction stir welding (FSW) and Coulomb friction work theory, the residual stresses field of FSW joints of 6N01 aluminum alloy (T5), which was used in high speed train, were calculated by using the ANSYS finite element software. During the FEM calculation, the dual heat source models namely the body heat source and surface heat source were used to explore the evolution law of the welding process to the residual stress field. The method of ultrasonic residual stress detecting was used to investigate the residual stresses field of the 6N01 aluminum alloy FSW joints. The results show that the steady-state temperature of 6N01 aluminum alloy during FSW is about 550 ℃, and the temperature mutates at the beginning and at end of welding. The longitudinal residual stress σx is the main stress, which fluctuates in the range of -25 to 242 MPa. Moreover, the stress in the range of shaft shoulder is tensile stress that the maximum tensile stress is 242 MPa, and the stress in the outside of shaft shoulder is compressive stress that the maximum compressive stress is 25 MPa. The distribution of the tensile stress in the welding nugget zone (WNZ) is obviously bimodal, and the residual stress on the advancing side is higher than that on the retreating side. With the increasing of the welding speed, the maximum temperature decreased and the maximum residual stress decreased when the pin-wheel speed kept constant. With the increasing of the pin-wheel speed, the maximum temperature of the joint increased and the maximum residual stress increased when the welding speed was constant. The experimental results were in good agreement with the finite element results.