Friction stir processing (FSP) is an effective technique for surface modification and grain refinement. This method can be used to incorporate hard ceramic reinforcement into modified aluminum surfaces, allowing for the fabrication of composites with enhanced properties. In this study, FSP was utilized to fabricate surface composites of aluminum alloy 6061-T6 reinforced with zirconium-silicate particles. The effects of tool rotational and traverse speeds, as well as the number of passes, on the microstructural and mechanical properties of the composite specimens were investigated. The corresponding strength, grain size, and microhardness of the specimens were evaluated and compared with unprocessed and non-reinforced aluminum alloy. The scanning electron micrographs of the specimen cross-section showed an excellent dispersion of zirconium-silicate particles in the aluminum matrix, indicating the homogeneity of the aluminum composite and the success of the applied FSP. The results showed that increasing the number of passes from one to four caused microstructure refinement at the stir zone, resulting in enhanced tensile strength and hardness of the produced composite. An optimum value of 1000 rpm and 20 mm/min for rotational and traverse speeds was obtained. Consequently, a composite with improved mechanical properties was achieved due to the formation and distribution of reinforcing zirconium-silicate particles. Manuscript profile