Microstructure and crack propagation behavior of 2195 Al–Li alloy with different orientations in the friction stir welding nugget zone

The 2195 Al–Li alloy is widely used in the aerospace field, where using friction stir welding technology can achieve lightweight and reduced wear designs for components. Fatigue failure, as one of the main modes of damage affecting the life and reliability of structural components, is particularly significant. This paper thoroughly explores the differences in microstructure and fatigue crack propagation behavior between the advancing side and retreating side of the friction stir welded joint in different sampling directions, providing a theoretical basis for enhancing the fatigue performance of friction stir welds. Characterization of the microstructure of the samples was performed using Electron Backscatter Diffraction (EBSD) and X-Ray Diffraction (XRD), and the fatigue properties were investigated using fatigue crack propagation rate curves and crack growth rate curves. The results indicate that the longitudinal base material grains tend to a fibrous structure, while the axial base material grains are distributed in a lamellar fashion. Compared to the advancing side of weld nugget zone, the retreating side of weld nugget zone has significantly reduced grain size and texture types. The fatigue performance of the retreating side of the weld nugget zone is superior to that of the advancing side, and the circumferential welds outperform the longitudinal welds in terms of fatigue performance.