Effect of weld curvature radius and tool rotation direction on joint microstructure in friction stir welding casting alloys

Curved welds were designed and the effects of the weld curvature radius and tool rotation direction on the microstructure of friction stir welded cast aluminum alloy joints were investigated. Results show that both the weld curvature radius and tool rotation direction have a significant influence on the microstructure of the curved joints during FSW. With decreasing weld curvature radius, the size of the tunnel defect is reduces and the proportion of fine Si particles in the stir zone increases. Si particles are finer and denser in the retreating side (RS) than that in the advancing side (AS) when both the welding direction and tool rotation direction are anticlockwise. However, when the welding direction is anticlockwise while the tool rotates clockwise, the proportions of fine Si particles decrease compared to the former situation. Furthermore, the tunnel defect is more likely to be present in the AS in the former situation.