Microstructural heredity and its effect on mechanical properties of linear friction welded Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy joints

The Ti-6.5Al-3.5Mo-1.5Zr-0.3Si blocks with three different original microstructures obtained by heat treatment, were joined successfully with linear friction welding (LFW). The microstructure evolution and mechanical properties were investigated in detail to clarify the microstructural heredity during welding process for the first time. Results show that all joints contain a weld center zone (WCZ), thermomechanically-affected zone (TMAZ) and base metal (BM) of different sizes. The microstructure heredity during LFW is partial. All three WCZs contain fine β grains with acicular α laths of similar texture distribution indicating no microstructural heredity in this area. Similar dynamic recrystallization process happens during LFW in three joints, and the β grain size in BM has no effect on the final grain size in WCZ. While the material in the TMAZ shows partial phase transformation and deformation compared with the original microstructural characteristic of BM. The similar microstructures across the WCZ of the three joints produce similar hardness as that of the water-quenched base metal. The different microstructures in the TMAZ and the BM produce different hardness distributions and different fracture modes during tensile strength testing.