**Abstract**

In this investigation, the vibration of the workpiece is accompanied by the rotating movement of the tool during friction stir spot welding. The method is entitled to friction stir spot vibration welding (FSSVW). Al5083 alloy samples are joined by two welding methods, friction stir spot welding (FSSW), and FSSVW under different plunge depths (DP). The microstructures and fracture surface of the welded zones were analyzed by optical microscopy (OM) and scanning electron microscopy (SEM), respectively. Analyzing the microstructures and mechanical properties of welded samples in both methods revealed that weld region grain size reduced and its hardness increased as the mechanical vibration and high plunge depth have been applied. In addition, the strength and ductility values of FSSV welded specimens with high plunge depth were higher than those produced by FSSW under low plunge depth. Furthermore, it was concluded that the effect of vibration on microstructure and mechanical properties of welded specimens increase as vibration frequency is increased.

**Keywords:** friction stir spot welding, mechanical vibration, mechanical properties, microstructure, grain size
