With changing amplitude,the dissimilar titanium alloys of TC11 and TC17 were welded by linear friction welding and the welded joint temperature was measured.The microstructure of the joints and flash were examined using an optical microscope(OPM) and a scanning electron microscope(SEM).Electron probe microanalysis(EPMA) was also carried out to determine the elemental diffusion in and around the interface region.The results showed that with increasing amplitude,the weld heat input increased and the flash length increased.During the linear friction welding,the temperature around the interface exceeded 1100℃,above βtransition temperature.Dynamic recrystallization is operative on weld center and the flash during linear friction welding.There still exists an evident interface after welding and no mechanical mixture was found at the interface.Compared to the parent material,the microstructure in the weld and flash center was refined.The size of the recrystal grain on both sides of the welded joints decreased with increasing amplitude.Elemental diffusion layers exist on the interface and with the amplitude increased the thickness of the diffusion layer become wider.