Fatigue crack nucleation and microstructurally small crack growth mechanisms in high strength aluminum alloys

•Surface replica method was used to measure small fatigue crack growth rates.•Fatigue cracks initiated from voids, particles and PSBs.•Grain misorientation was quantified at crack initiation site. Characterization of microstructurally small fatigue crack growth behavior for two aluminum alloys, AA7065 and AA2099, were quantified using a surface replication process for the first time. In addition, scanning electron microscopy analysis revealed that for AA7065, crack initiation was caused by either voids or intermetallic particles. Whereas, for the AA2099, crack initiation was caused by persistent slip bands and intermetallic particles. From electron backscatter diffraction results, the grains at the crack initiation site for the AA7065 exhibited high misorientation boundaries, while the grains at the crack initiation sites for the AA2099 exhibited both high and low misorientation boundaries.