Effect of Ultrasonic Impact on Corrosion Fatigue Properties of Titanium Alloy Welded Joints

Ultrasonic impact treatment (UIT) is widely used in the aerospace field as a surface treatment technology. The effect of UIT on the corrosion rate and corrosion fatigue properties of TC4 titanium alloy laser welded joints was investigated in this study. On this basis, the surface roughness, surface morphology, microstructure, microhardness and residual stress of samples treated with two different UIT amplitudes (18 and 25 pm) were analyzed. The results showed that compared with the untreated sample, the surface roughness of UIT-treated specimens was increased by 3.9 times but the surface scratches were eliminated. The surface grains of specimens were refined to form a plastically deformed layer similar to 110 mu m thick. Compared with the untreated specimens, the hardness of UIT treated specimens were increased by 13.2%, and the hardness influence depth was 0.06 mm. In addition, a high level of compressive residual stress (- 529 MPa) was introduced on the surface layer of the specimen. UIT reduced the corrosion rate of the specimen, but the higher UIT amplitude, the worse the reduction effect. UIT treatment improved the corrosion fatigue life of specimens, and the higher UIT amplitude, the more obvious the effect of improvement. The fatigue fracture of the specimens was analyzed by scanning electron microscope. It can be observed that for UIT treated specimens, the fatigue crack source was suppressed inside, the fatigue fringe spacing was reduced, and the dimples were enlarged. Finally, the strengthening mechanism of UIT on the corrosion fatigue properties of the specimens was proposed.