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In this research, dissimilar AA2024-T351 to AA7075-T651 joints manufactured at high heat input by friction stir welding has been studied to analyze the microstructure and mechanical properties by employing post-weld heat treatment (PWHT, solution and subsequent various aging treatments). The results revealed that abnormal grain growth (AGG) occurs in the nugget zone (NZ) of the joints after PWHT compared to large numbers of fine equiaxed grains forming in the NZ of the as-welded joint. The degree of grain growth of AA2024 side at the interface is obviously higher than that of AA7075 side. Stable {111}1¯1¯2A1∗ and {111}112¯A2∗ simple shear texture components are presented in the bottom interface zone, which are not altered during PWHT. The joint performances subjected to five kinds of PWHT are not improved by PWHT due to the weak lack of penetration phenomenon between the two BMs in the bottom zone of the joints, which results in the fracture locations of all the six joints occurring in the NZ.