Effect of welding parameters on microstructure characteristics and fatigue properties of dissimilar joints prepared by linear friction welding on TC11 and TC17 titanium alloys

Linear friction welding (LFW) was conducted on TC11 (Ti-6.5Al-3.5Mo-1.5Zr-0.3Si) and TC17 (Ti-5Al-2Sn-2Zr-4Mo-4Cr) titanium alloys shaped in the rectangular section of 75 mm × 20 mm, in which the welding parameters were set as oscillation frequency 20–60 Hz with amplitude 2–3 mm, friction pressure 58.8–65.3 MPa with friction time 3–5 s, and upset pressure 49–78.4 MPa with upset time 30 s. The microstructure characteristics and fatigue limit were measured and analyzed. After LFW, a microstructure change occurs with martensite in the weld zone and elongated grains in the thermo-mechanically affected zone. The effect of amplitude and frequency on fatigue properties is larger than that of friction time and forging pressure. With the amplitude and frequency of oscillation increasing, the fatigue limit increases firstly and then decreases. Accordingly, the optimal parameters were gained. The change tendency of α phase at failure location with the welding parameters could well describe the fatigue limit. Meanwhile, the fracture surface of joints presents a composite fracture of the quasi-cleavage, fatigue striations, and dimples. The spacing of fatigue striations firstly becomes smaller and then larger with the amplitude increasing which agrees with the change of fatigue limit.