Effect of Tool Geometry on Material Flow Behavior of Refill Friction Stir Spot Welding

Using LY12 aluminum alloy as the research object, material flow behavior of refill friction stir spot welding process is simulated. The simulation results are investigated by studying the macrostructure and microstructure of the refill friction stir spot welding joints. Effects of tool geometries on material flow are mainly discussed. Results show that bonding ligament and grains in different regions of the stir zone are affected by the material flow behavior. Rational groove on the sleeve can increase the material flow velocity. From the viewpoint of reducing the unfavorable bonding ligament, the groove on the sleeve inner wall is better than the smaller width groove on the sleeve outer wall. Compared with the concentric circle grooves on the sleeve bottom, the scrolled groove is more beneficial to decrease the bonding ligament thickness and increase the welding spot area. Disregarding the higher heat input, sleeve with bigger outer diameter greatly increases the flow velocity and the welding spot area compared to changing the groove geometry.