The purpose of investigating friction stir welding for flange joints is to provide a strong and suitable alternative to arc welding, resulting in enhanced mechanical characteristics of welded joints. One major challenge in commercializing friction stir welding( FSW) for flange joints is the complexity of weld path and fixture design. In this study, FSW welded joints were performed on flange joints using uniquely developed fixtures designed to securely hold the pipes and plates. The focus of the research is on optimizing the multi-performance properties of the FSW of Al 6063-T3 using the hybrid Grey-TOPSIS based Taguchi method. The L9 Taguchi orthogonal array was utilized to maximize the FSW rotation speed, travel speed, and tool profile. The mechanical properties of the weld zone were used to evaluate the integrity of the welded joint. The results showed that the best parameter setting for the FSW process was found to be a rotation speed of 3 000 r/min, a travel speed of 3 mm/min, a shoulder diameter of 30 mm, and a conical tool profile. At these settings, the material exhibited tensile strength, hardness, and a corrosion rate of 170 MPa, 63.7709 HV, and 0.022 mm, respectively. The rotation speed was identified as the most important process variable, contributing 82.01% to the multi-performance of the weldments. The Grey-TOPSIS based on Taguchi method was found to be a simple yet efficient method for optimizing several performance aspects of welded joints, as confirmed by an emphasis test conducted to evaluate the optimization process.