Aero engines serve as a critical indicator of national comprehensive strength and technological advancement. However, their performance enhancement poses considerable challenges to the manufacturing technologies of hot-end components. Hot-end structures undergo inertial friction welding, which effectively avoids the defects associated with fusion welding and has been widely adopted for high-quality joining of these structures. This study addresses the inherent process limitations of inertial friction welded joints, including strengthening phase dissolution within the welding zone (WZ), along with axial and radial microstructural heterogeneity, and proposes a customized post-weld heat treatment (PWHT) strategy for inertial friction welded joints of FGH96 superalloys. A systematic investigation was conducted on the effects of solution aging and double aging on microstructural evolution and mechanical properties. The results indicated that increasing the solution temperature leads to grain coarsening and enhanced recrystallization, accompanied by pronounced precipitation and growth of the γ′ strengthening phase, a more uniform carbide distribution, and intensified grain boundary serration within the WZ compared to joints at low solution temperature. At a solution temperature of 1140 ^oC, abnormal grain growth occurred, along with coarsening and inhomogeneous distribution of the γ′ strengthening phase. After solution aging, the impact toughness of the joints improved with increasing solution temperature, whereas the tensile strength initially increased and then decreased. At the solution temperature of 1080 ^oC, the grain size and γ′ strengthening phase were moderate and uniformly distributed, the degree of recrystallization and grain boundary serration were relatively high, carbides were uniformly dispersed, and microstructural inhomogeneity was notably improved. Under this condition, the ultimate tensile strengths of the joints at room temperature and 750 °C were 1455 and 1042 MPa, respectively; and the impact toughness reached 41 J/cm², demonstrating an optimal strength-toughness synergy. Double aging promoted the uniform precipitation of tertiary γ′ strengthening phase in the WZ, resulting in tensile strengths of 1574 and 1279 MPa at room temperature and 750 ^oC, respectively, approaching base metal levels. Meanwhile, the hardness was considerably enhanced beyond the base metal, although the impact toughness was slightly reduced compared with the as-welded joints.