In ultrasonic assisted friction stir welding (UaFSW) system, the ultrasonic vibration is exerted onto the tool radially, and can achieve synchronously thermo-mechanical action with the tool. A mathematical model is established to investigate the coupled “acoustic action-heat generation-plastic deformation” behaviors in UaFSW. The ultrasonic stress work is considered to revise both the constitutive equation and the slip rate. In UaFSW the ultrasound vibrates along the welding direction and the peak acoustic pressures at both leading and trailing sides enhance the material plastic flow there. It is found that the ultrasound increase the percentage of viscous dissipation heat in the total heat generation. It is the acoustic softening effect, not the supplemented ultrasonic energy, which plays a dominate role in UaFSW. The numerical results are compared and experimentally verified with the thermal cycle at typical positions and the cross section of weld zone respectively.

在超声辅助摩擦搅拌焊接（UaFSW）系统中，超声振动会径向施加到工具上，并且可以与工具同步实现热机械作用。建立了一个数学模型来研究UaFSW中耦合的“声学作用-生热-塑性变形”行为。超声应力功被认为可以修改本构方程和滑移率。在UaFSW中，超声波沿焊接方向振动，并且在前侧和后侧的峰值声压增强了那里的材料塑性流动。发现超声波增加了总发热量中粘性耗散热的百分比。在UaFSW中起主要作用的是声学软化效果，而不是补充的超声能量。