Abstract: In this paper,the models of Al-Cu heterogeneous friction stir lap welding with pin length of 2.4mm and 2.8mm were established by the method of computational fluid dynamics.Based on VOF method,the two-phase distribution of aluminum and copper was calculated,and the thermal-mechanical coupling effect of two-phase material flow under different pins was quantitatively analyzed.The interfacial friction shear stress and heat flow were calculated by the relative sliding state of the tool/workpiece contact interface.It was found that the increase of pin length could effectively enhance the mixing of two-phase materials,strengthen the plastic deformation,and enlarge the hook structure.With the increase of material flow,the interfacial friction shear stress decreases,which led to the decrease of frictional heat generation and interfacial heat flux.However,the enhancement of local plastic flow improved the viscous dissipation heat and temperature in the plastic deformation area,and the vertical migration of aluminum was more intense,which would increase the formation of intermetallic compounds.In addition,the accuracy of the model was verified by comparing the distribution of two-phase materials in the weld cross section with the literature experiment.