Progress in the Effect of Ultrasonic Impact Treatment on Microstructure Improvement and Strengthening Mechanism in Additive Manufacturing

Additive manufacturing (AM) is a rapidly developing technology that has found widespread use in the manufacturing industry. However, the application with high performance and stability requirements is constrained by its coarse microstructure, which exhibits obvious directionality during the deposition of metal parts. Ultrasonic impact treatment (UIT) has been recognized as an effective strengthening method that can improve the stress state, refine the microstructure, and enhance the overall performance of metal parts fabricated via AM. This paper summarizes the theoretical views and limitations of UIT strengthening regarding surface plastic deformation. Additionally, it elaborates on the mechanism of microstructure refinement and the transformation of columnar dendrites to equiaxed dendrites, influenced by the combined effect of UIT and AM. Finally, the paper outlines the problems and suggestions related to strengthening theory that require further investigation in the process of UIT-assisted AM.