Optimization of Heat-Treatment Process for Corrosion Resistance of Ti600/TC18 Inertial Friction Welding Joint

Ti600/TC18 dissimilar titanium alloy joints were prepared by inertia friction welding and then underwent stress-relief annealing and three-stage annealing. The microstructure and corrosion resistance of the joints were characterized through scanning electron microscopy and X-ray diffractometry, and were tested by electrochemical measurements and static immersion corrosion experiments in HCl solution with different concentrations. The results show that the microstructure becomes more refined with more grain boundaries after stress-relief annealing, while the secondary α phase is coarsened and the α phase in the grain boundaries is formed on the microstructure after three-stage annealing with fewer grain boundaries. The specimen treated by stress-relief annealing has excellent corrosion resistance due to the denser and stabler passivation film formed on the grain boundaries. When the stress-relief annealing process is defined as 650°C, 3 h, and air cooling, more grain boundaries appeared on the joint, and, as a result, it provides more nucleation sites for the formation of the passivation film, so it is endowed with a good ability to resistant corrosion.