The friction stir spot welding (FSSW) process is a solid-state welding technique recognized as one of the most significant advancements in metal joining over the past decade. In this study, the effects of rotational speed and tool contact time, with a unique design different from previous research, on the microstructure and mechanical properties of 5754 series aluminum alloy were investigated. The workpiece was clamped using a specialized fixture on a radial drilling machine, and welding operations were performed using a FSSW machine at different rotational speeds and various tool contact times. Subsequently, the microstructure, microhardness, and tensile-shear strength of the welded spot region were evaluated. The results showed that increasing the tool rotational speed and prolonging the tool contact time led to an improvement of approximately 105% in the tensile-shear strength. According to statistical analyses, the factors of rotational speed and tool contact time significantly affected the shear strength with a confidence level greater than 95%; however, statistical analyses revealed different results regarding the relationship between rotational speed, contact time, and hardness.
