Abstract: The addition of IN718 alloy as an interlayer effectively reduces the high-temperature ductility-dip cracking susceptibility in ultrasonically excited TIG joints of IN690 nickel-based alloy, and the joint needs to undergo heat treatment to regulate its microstructure composition. By implementing different post-weld heat treatment processes, this study investigated the influence of solution temperature on the joint’s microstructure, precipitate distribution, and mechanical properties. Results show that solution heat treatment promotes grain coarsening in both the weld and base material while inducing carbide segregation along grain boundaries. Results show that solution heat treatment promotes grain coarsening in both the weld and base metal while inducing carbide segregation along grain boundaries. With increasing solution temperatures during the solution + double-aging heat treatment, significant carbide coarsening at grain boundaries is observed across all specimens. The microhardness of joints subjected to 1150 ℃ solution + double-aging heat treatment approximates that of as-welded specimens, while specimens treated at 980 ℃ and 1050 ℃ solution + double-aging exhibit 10 ~ 20 HV hardness increments compared to the as-welded condition. Specimens processed with 1050 ℃ solution + double-aging demonstrate optimal mechanical performance, post-fracture elongation of 38.4% and tensile strength of 630 MPa. Their fracture surfaces exhibit uniformly distributed equiaxed dimples, indicative of ductile fracture and transgranular failure modes. Comprehensive analysis of microstructural evolution and mechanical test results confirms that the 1050 ℃ solution + double-aging post-weld heat treatment process enables IN690 joints incorporating IN718 interlayers to achieve optimal comprehensive properties.