This research presents a pioneering investigation into friction stir processing (FSP) of different aluminum alloys reinforced with silicon nitride powders (Si3N4). By optimizing FSP parameters, such as stir tool profile and cooling medium, this study aims to enhance the microstructure and mechanical properties. The findings of this research contribute to the development of advanced FSP techniques for improving the performance of these alloys in different industries. FSP of three aluminum alloys (1050, 2011, and 6063) reinforced with Si3N4 powders was conducted under different processing parameters was investigated. Tensile tests and hardness evaluations were conducted to assess the mechanical properties. The best combinations of processing parameters were defined using the Taguchi L27 orthogonal array, while a response surface methodology (RSM) with a central composite design of three factors and three levels was employed to develop the relationship between the FSP parameters (material type, pin profile, and cooling rate). The selected outputs included yield strength (YS), ultimate tensile strength (UTS), hardness (Hv), and elongation percentage (El%). An analysis of variance (ANOVA) was conducted to identify the significant process parameters affecting the responses. The results after FSP on Al plates indicate that the optimum UTS and YS values are achieved by performing FSP on 2011 AA with a conical pin profile and under indirect air-cooling. The highest hardness value was obtained under the same conditions but with indirect R-410 A cooling. Conversely, the optimum value of El% was reached by conducting FSP on 1050 AA with a cylindrical pin profile and indirect R-410a cooling. The maximum UTS, YS, El, and HV values are 286 MPa, 167 MPa, 40%, and 118 HV, respectively. Material type (M) was the primary dominant parameter affecting mechanical properties, while the cooling media ranked second.