Superplastic Deformation Behavior of Friction Stir Welded Ti-4.5Al-3V-2Fe-2Mo Alloy

SP700 titanium alloy (Ti-4.5Al-3V-2Fe-2Mo) has excellent superplasticity and relatively wider hot working map at low temperature. This paper used two method to study superplastic deformation behavior of the joint of FSW (friction stir welding) SP700 titanium, as maximum m value method and constant strain rate method. The results showed that a elongation of 989.9% was obtained at 795℃ with maximum m value method; and a elongation of 687% was obtained at 795℃ and 5×10-4 s-1 with constant strain rate method. The optimum superplastic deformation temperatures were all higher than that of base materials by two methods. Compared with the finer microstructure at nugget zone of FSW, the grains grew seriously after superplastic deformation, and the volume of beta phase comparably decreased. The reason for the coarse grains after SPF was because the finer grains had higher distortion energy, and during SPF process the potential energy for the grain growing comparably highly increased. The deformation mechanism at higher strain rate was that grains were elongated, grown, fractured and equixed recrystallization. Microstructure in NZ (nugget zone) and TMAZ (thermo-mechanically affected zone) of FSW joint was obviously non-uniform, however, it could be effectively improved after superplastic deformation. © Editorial Office of Chinese Journal of Rare Metals. All right reserved.