Optimization of welding parameters for the reverse dual-rotation friction stir welding of a high-strength aluminum alloy 2219-T6

As for high-strength aluminum alloys such as 2219-T6, the friction stir welding (FSW) has the capability to reduce the thermal effect and obtain better joint property when compared with conventional welding processes, but its welding thermal cycle is sufficient to change the original strengthening precipitates and deteriorate the joint property. The reverse dual-rotation friction stir welding (RDR-FSW) has been demonstrated to be available for improving the joint property further due to its capability to adjust the heat generation through the separately designed tool shoulder and tool pin. Moreover, the welding torque exerted on the workpiece by the reversely rotating shoulder is opposite to that exerted by the rotating tool pin, thus the total welding torque is reduced, and this is beneficial to reduce the clamping requirement and broaden its application. In the present paper, the optimization experiment of RDR-FSW was conducted on the high-strength aluminum alloy 2219-T6 according to the Box-Behnken design method, aiming to obtain the optimum welding condition and the corresponding optimum tensile strength. A mathematical response model was developed based on the optimization experiment. Applying the RDR-FSW, the optimum tensile strength of 357 MPa was obtained, and this is obviously higher than the optimum tensile strength obtained by the conventional FSW and approaches the optimum tensile strength obtained by the underwater FSW which is also proposed to improve the joint property further.