Abstract: Finite element method is used to analyze the 3D flow of Al 6061-T6 in friction stir welding (FSW). The effect of the variation of the translational velocity on the material flow and the equivalent plastic strain are also studied. Results show that the material in front of the pin moves upward due to the extrusion of the pin and is forced to rotate around the pin and then, the material behind the pin is forced to move downward, which makes the friction stir process continuing. A good correlation between the equivalent plastic strain and the microstructure zones is found. With the increase of the translation velocity of the pin, the flow of the material in friction stir welding becomes faster but the equivalent plastic strain decreases. The lower translational velocity can improve the coalescence of the welded plates.

Key words: friction stir welding, material flow, finite element, equivalent plastic strain, microstructure