Statistical study for grain orientation effects on fatigue damage in Al-Mg polycrystals via multiscale characterization

The accumulation of fatigue damage during cyclic loading is typically localized and heterogeneous, owing to the intrinsic inhomogeneous microstructure of polycrystalline materials. This study systematically analyzed the correlation between surface fatigue damage accumulation, grain orientation and dislocation slip activity through an in-situ fatigue test conducted on 1018 grains in Al-Mg alloy. Multiscale characterization including atomic force microscopy, confocal laser scanning microscopy, transmission electron microscopy and electron backscatter diffraction, as well as numerical analysis revealed that the generation of severe persistent slip markings (PSMs), with surface extrusion heights exceeding 200 nm, requires three specific conditions: (i) activation of both primary and secondary slip systems, (ii) a favorable spatial orientation of their Burgers vectors with respect to the specimen surface, and (iii) enhanced dislocation activity on cross-slip systems. Based on these observations, we established an assessment framework that uses initial grain orientation to identify grains susceptible to high accumulation of fatigue surface damage. This method provides a practical and useful means to evaluate the weak regions in polycrystalline materials under cyclic loading, while also offering a valuable reference for simulating fatigue damage in these materials.