It is an underlying fact for the case of the joining process especially welding to have optimized parameters to achieve joints with outstanding mechanical characteristics. In the current article, using stir-cast aluminum-based alloy (Al 6061) is stir-cast with Al 6061/5%wt. silicon carbide, Al 6061/10%wt. silicon carbide, and Al 6061/18%wt. silicon carbide was welded using an underwater friction-stir welding process. Optimum welding parameters [namely, tool rotating speed (N), welding speed (S), and silicon carbide (SiC)] are investigated using analysis of variance (ANOVA) and response surface methodology (RSM) statistical approaches. High ultimate tensile strength and microhardness were set as required characteristics of quality welds. Since there are two responses and two objectives, multiple-criteria decision-making approach—response surface methodology was performed alongside ANOVA. Optimal parameters from these statistical approaches are converged to a tool rotating speed of 1,736.36 rpm, a welding speed of 11.58 mm/min, and a SiC of 16.67%, respectively. For the current inquiry, the computed ultimate tensile strength and microhardness are 984 MPa and 89.9 HV, respectively, and these values are congruent with the findings of effectiveness studies. It is deduced from this s