The solid-state nature of friction stir spot welding process provides outstanding advantages for the sound joining of aluminum alloys. Within this study, 3 mm-thick AA5052-H32 sheets are successfully joined by friction stir spot welding using 2344 hot-worked steel pin to investigate the effects of various tool plunge depths on the microstructure, mechanical and metallurgical properties of similar welds. Therefore, the experiments are performed at different plunge depths in the range of 3 mm-4 mm. Accordingly, the relationships between the process parameter (tool plunge depth) and the responses (microstructure, dome structure, microhardness and lap shear tensile load) are established. Microstructure analyses demonstrate that the increase in the plunge depth leads to more grain refinement within the stir zone, which significantly affects the mechanical performance of the similar joints. This study also indicates that the tool plunge depth in friction stir spot welding process has a noteworthy influence on the characteristic features of the 5052 aluminum alloy joints, such as the dome structure. Moreover, an explicit increase in the microhardness towards the weld stir zone is observed in all specimens. It is found that the average maximum tensile-shear force enhances with the increment in the tool plunge depth from 3 mm to 4 mm.