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Heat treatment at different temperatures was carried out on a Ti3Al linear friction welding joint. The characteristics and evolution of the microstructure in the weld zone (WZ) and the thermo-mechanically affected zone (TMAZ) of the Ti3Al LFW joint were analyzed. Combined with the heat treatment after welding, the effect of the heat treatment temperature on the joint was discussed. The test results indicated that the linear friction welding (LFW) process can accomplish a reliable connection between Ti3Al alloys and the joint can avoid defects such as microcracks and voids. The weld zone of the as-welded Ti3Al alloy joint was mainly composed of metastable β phase, while the TMAZ was mainly composed of deformed α2 phase and metastable β phase. After being heat treated at different temperatures, the WZ of the Ti3Al LFW joint exhibited a significantly different microstructure. After heat treatment at 700 °C, dot-like structures precipitated and the joint microhardness increased significantly. Subsequently, the joint microhardness decreases with the increase in temperature. Under heat treatment at temperatures above 850 °C, the formed structure was acicular α2 phase and the joint microhardness after heat treatment was lower than that of the as-welded joint.

In this paper, the fracture toughness of the thermo-mechanically affected zone (TMAZ) and the weld zone (WZ) of the TC17 titanium alloy linear friction welding joint was studied. The relationship between microstructure and fracture toughness of the joint, as well as the morphologies of the joint microstructure and fracture were investigated. The results indicate that after heat treatment, there was no significant difference in hardness between the WZ and the TMAZ of the joint, which was about 420 HV. However, the microstructures of the different zones of the joint were significantly different. The TMAZ was composed of coarse grains having an internal basket-shaped α phase with an uneven grain size, while the WZ was composed of relatively uniform fine grains and contained a sheet-like α phase. The fracture toughness of the TMAZ was found to be higher than that of the WZ, indicating that the microstructure of the joint had a significant impact on the fracture toughness. In addition, the fracture resistance of the TMAZ with coarser grains and uneven microstructure was better than that of the WZ with fine grains and uniform microstructure.

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