Effect of tool ratio on the performance of 6061-T6 aluminum alloy refill friction stir spot welded zone

The refill friction stir spot welding (RFSSW) of defect-free aluminum alloy was performed using a fixed-diameter shoulder and probes of different diameters. The process parameters were set at a rotational speed of 1400 rpm and welding speeds of 30 mm/min, 40 mm/min, and 50 mm/min. The results showed that the grain size in the weld zone was refined. The joint residual line (JRL) did not affect the ultimate lap shear force (ULSF) of the weld zone. A higher “HOOK” height increased the ULSF by avoiding the load plane. As a result, the ULSF was high at different welding speeds for larger probe diameters. It was not sensitive to process parameters. However, the hardness was lower.