Relationship between Stress State and Microstructure of 7B04 Aluminum Alloy Surface Fatigue Properties by Laser Shock Peening Improvement

Fatigue performance is always an important factor affecting the application of aluminum alloys. The service life of the 7B04 aluminum alloy tends to reduce under continuous alternating loads. Therefore, a new method is urgently needed to improve fatigue performance. Laser shock peening (LSP) is a widely proposed method to enhance fatigue performance. It is found that LSP can prolong the fatigue life of 7B04 by improving the surface stress state. During the strengthening process, the residual stress is mainly attributed to the change in microstructure, which the statistical results of grain size can reflect. The microhardness of the treated 7B04 is 22.7% higher than that of the untreated sample. In addition, there is a significant residual compressive stress from the specimen surface to its interior of about 1500 µm after the process of laser shock peening. The fatigue life is extended to 93%, and the ultimate fracture changes macroscopically. The fatigue performance of 7B04 is greatly improved by the LSP treatment. The strengthening mechanism of LSP is established to reveal the relationship between microstructure and stress state to improve the fatigue performance of metal parts of any shape.