In this analysis, friction stir processing (FSP) was applied to the Si rich TIG welded joint to study the influence of multi-pass FSP (MPFSP) on microstructure, hardness and tensile properties. The TIG welding defects (coarse grain structure, porosity, microvoids, and solidification cracking) were eliminated, and the grain size of the TIG welded joint was decreased. As the FSP passes increases, the coarse eutectic Mg2Si and Al13Fe4 phases are converted into small phases. The coarse and elongated dendrite structure of the TIG welded joint was decreased after one FSP pass. The homogenization or modification of the primary α-Al exists in the TIG weldment was continuously improved as the TIG + FSP pass increased. The SZ of TIG + 3 pass FSP showed ultrafine grains of 3.42 µm compared to other welded specimens. The average ultimate tensile strength (UTS) of the TIG welded joint with filler ER4043 was observed to be 79.82 MPa, whereas the UTS of TIG + 1 pass FSP, TIG + 2 pass FSP, and TIG + 3 pass FSP was 97.87 MPa, 120.36 MPa, and 126.92 MPa respectively.