Research on fatigue behavior of the flash welded joint enhanced by ultrasonic peening treatment

Nanocrystallization process is that the coarse grains are refined to the small-sized dislocation cells under the action of ultrasonic peening treatment (UPT). Dislocation tangling and dislocation wall are formed as a result of dislocation aggregation at grain boundaries. Dislocation tangling and dislocation wall were turned into the small-sized subgrains by absorbing dislocations. With further increasing of strain energy, dislocation tangling and dislocation wall are formed again in the refined subgrains and grains. The above microstructural evolution is repeated in refined subgrains and grains, which bring further refinement of those grains. Surface nano-enhancing will effectively improve fatigue performance of the flash welded joint.73