Study On Ultrasonic Assisted Friction Stir Welds Of Numerical Simulate And Residual Stresses For Aluminum Alloys

Ultrasonic assisted stir friction welding (UAFSW), which can improve the welds performance by attaching an ultrasonic effect to the welding, is a new metal solid-state welding technology basing on friction stir welding. Existing research has focused on the ultrasonic assisted friction stir welding process to improve weld performance, improve weld quality. Its mechanism is not carried out in-depth research. In order to better grasp of its mechanism, and thus play its technological advantages, it is necessary to conduct in-depth studies of ultrasound-assisted friction stir welding mechanism.Using numerical simulation and experimental method,2024aluminum alloy was welded by UAFSW to study the mechanism of UAFSW and reveal the mechanism of ultrasonic to improve the weld properties. First, based on computational fluid dynamics and theory of elastic-plastic mechanics, a heat-force-flow coupled numerical model of UAFSW was built. Secondly, the numerical model was verified by welding process, the welding temperature test and metallographic analysis of2024aluminum. Finally, residual stress distribution and deformation control mechanism of UAFSW was researched.By numerical simulation analysis, the following conclusions of UAFSW were found:(1) the weld surface temperature of UAFSW is higher than FSW, because of the heat input was increased by the ultrasonic, and the welding process window is expanded by UAFSW;(2) plastic material flow can be driven by Ultrasonic, which increasing the cooling speed of material and leading to a large temperature gradient along the thickness direction than FSW;(3) through the flow field analysis, it is found that velocity gradient of advancing side is larger than the retreating side; the velocity gradient of advancing side is increasing with the welding speed, and the advancing side become weak point of the weld because of the lack of the material. The reliability and accuracy of the numerical model was proved by2024aluminum welding temperature testing, tensile testing and microstructure observation. Experiment studied on the ultrasonic’s impact on the residual stress of UAFS W was implemented. It was found that the residual stress can be effectively controlled by UAFSW, and the longitudinal residual stress reduces about30%by UAFSW compared to FSW. The low welding speed, low rotational speed, and small diameter of the pin shoulder can reduce the residual stress. Based on the results, the sheet deformation mechanism and the control method during UAFSW were studied as well. It is found that the welding deformation can be effectively controlled by UAFSW, and it can also be controlled by reducing the diameter of the pin shoulder and increasing the mandatory water-cooled could be able to control the welding deformation. These results are useful to realize the welding of sheet metal with small deformation.