Numerical simulation for the comparison of thermal and plastic material flow behavior between symmetrical and asymmetrical boundary conditions during friction stir welding

Abstract

An accurate description of the contact condition between the tool and the workpiece material is one of the most important issues for expounding the underlying multi-physics coupled mechanism during friction stir welding (FSW) process. In the present study, a novel asymmetrical boundary condition around the tool-workpiece contact interface is proposed for the FSW of AA2024-T4 alloy. A three-dimensional computational fluid dynamics model is employed for the comparison of the coupled thermal and plastic material flow behavior between asymmetrical and symmetrical boundary conditions. Numerical results of heat generation, temperature distribution, tunnel defect formation and material flow streamline during the welding process are quantitatively analyzed. Besides, various experimental measuring methods are utilized to obtain information about temperature, thermal cycle, tool torque and horizontal cross-section around the exiting keyhole. It is revealed that the modeling results of heat flux density and temperature distribution around the pin, as well as material flow characteristics all change significantly for the two models with different boundary conditions. Particularly, the asymmetrical boundary condition is more capable of predicting temperature fluctuation, plastic material flow along the vertical direction, as well as tunnel defect formation during FSW. Therefore, the superiority of the model with asymmetrical boundary condition over the symmetrical one during the numerical simulation of FSW is elucidated.

Keywords

Friction stir welding (FSW) / Numerical simulation / Heat generation / Plastic material flow / Asymmetrical boundary condition