Abstract: Inertia friction welded Ti₂AlNb alloy joints are subjected to heat treatment. The effects of different heat treatment processes on the microstructure and mechanical properties of welded joints are analyzed. The results indicate that base metal shows a typical microstructure comprised of α₂, B2 and O three phases. Base metal of aging treatment shows a typical microstructure comprised of B2+O phases. The microstructure of weld zone(WZ) and thermo-mechanically affected zone(TMAZ) of welded joints is main B2 phase. After double aging treatment, most B2 phase of WZ and TMAZ has transformed to network O phase in grain boundary and the needle with massive O phase within the grain. After aging treatment, O phase is not found in the grain boundary of WZ and TMAZ, and B2 phase transform into close and lamellar eutectoid structure of B2+O phase. The microhardness distribution of the joints in the three heat treatment states is basically the same in all areas. Double aging after welding improves the precipitation of O phase and forms an precipitation strengthening, which improve the microhardness of joints. The tensile strength of welded joint of solid solution before welding and double aging treatment after welding is the highest and is 1 193 MPa at room temperature. Tensile fracture of double aging after welding is mainly quasi cleavage fracture, that the room temperature tensile fracture of the joints of single aging after welding is mainly cleavage fracture, which the size of cleavage plane is relatively large. The tensile strength of joints of solid solution before welding and double aging treatment after welding is still the highest and is 986 MPa at 650℃ high temperature, and shallow dimples can be observed on the fracture that it is ductile fracture along grain boundary. However, the fracture morphology of joints of solid solution and aging treatment before welding is basically the same. The fracture form of the joints is mainly cleavage fracture and contains a small amount of quasi cleavage fracture.

Key words: Ti₂AlNb, inertia friction welded, microstructure, mechanical property