Abstract: The microstructure evolution in Ti₂ AlNb/TC11 dual alloys after near thermal forging, gradient heat treatment and thermal exposure at 550℃ for 50 h and 100 h, respectively, was investigated with optical microscope(OM) and transmission electron microscope(TEM). The results show that B2→O+β decomposition occurred in the welded seam and Ti2 AlNb matrix, and α₂ phase migrated to the grain boundary of B2 during thermal exposure. The time for thermal exposure was longer, the segregation of α₂ phase at grain boundary was severer. And α₂ phase agglomerated into block when the thermal exposure time was 100 h. Also, the β phase grew coarse and its volume percentage increased simultaneously. If Al and Nb contents were large in the joint, α₂ phase would agglomerate at grain boundary, the original O phase overprinting with the secondary O phase decomposed from B2 phase would coarsen.