Laser shock peening optimized microstructure stabilizes compressive residual stress to improve fatigue performance of high-strength aluminum alloy hole structure

Abstract

Hole structures are prone to fatigue cracks due to stress concentration during complex service conditions, making it difficult to meet the high safety and reliability requirements for the high-speed aircraft. In this study, laser shock peening (LSP) was used to modify the microstructure and residual stress of the 7050 aluminum alloy hole structure to improve fatigue life. Results showed that LSP could generate the network of low-angle grain boundaries (LAGBs) and ultra-high-density dislocations within coarse grains, and induce the re-precipitation of strengthening phases near the grain boundaries. Coarse grains with a low Schmid factor required multiple LSP to generate more intense plastic deformation and produced noticeable microstructural improvements. The LAGBs, dislocation tangles, and at the grain-boundary precipitates hindered localized plastic deformation during fatigue cyclic loading, thereby enhancing the stability of high-amplitude (−293 MPa) and deep (∼2 mm) compressive residual stress (CRS) generated by multiple LSP. The synergistic effect of surface microstructural strengthening and stable CRS significantly improved the fatigue life of hole structure.