Scale effect of pin on friction stir welding

Finite element method was used to study the material behavior and the residual stress distributions during the friction stir welding process. The results show that the flow of the material in the tangent direction takes the main contributions to the movement of the material in the friction stir welding process. A fluidized bed of material flow comes into being around the pin. With the increase of the pin's diameter, the laminar flow becomes much easier to be observed. The maximum of the longitudinal residual stress occurs in the boundary of the heat affected zone. The double peak feature of the longitudinal residual stress can be found. The region of the large residual stress becomes wider when the diameter of pin is increased.