The effects of two different grain structures on fatigue crack propagation (FCP) behavior of an Al-Cu-Li alloy were investigated. The results indicate that the fibrous grained and equiaxed grained samples exhibit significantly different FCP resistances. The FCP rates are particularly different at the Paris stage at the stress intensity factor range (ΔK) is about 20 MPa∙m1/2, the equiaxed grained sample is 8.23 × 10-4 mm/cycle, while the fibrous grained sample is up to 1.65 × 10-3 mm/cycle. The results of electron backscattered diffraction (EBSD) analysis of the crack propagation paths show that about 58.7 % of crack paths are transgranular and 67.6 % of the cracks are deflected in the fibrous grained sample, most crack segments are parallel to {111} 〈101〉 slip system. While in the equiaxed grained sample, the probabilities of transgranular and intergranular propagation are both about 50 % and 73.2 % of the cracks are deflected, most crack segments are parallel to {111} 〈011〉 slip system. The grain reference orientation deviation (GROD) and the kernel average misorientation (KAM) maps show that the degree of deformation at the grain boundaries of the fibrous grained sample is higher than the equiaxed one.

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