Slip band formation in plastic deformation zone at crack tip in fatigue stage II of 2xxx aluminum alloys

Analysis of the plastic deformation zone at crack tip in fatigue stage II of AA2524-T4 and AA2297-T87 alloys reveals the complex microstructural effects, such as second-phase particles, grain boundaries, Schmid factor and grain orientations, on the formation of slip bands. In AA2524-T4 alloy, slip band formation in plastic deformation zone relies mainly on grain orientation and boundary component. Goss, P and Q grains with low Schmid factor are hard to deform plastically, leading to few slip bands. Cube, S, R, Copper and Brass grains with high Schmid factor tend to form evident slip bands. However, if these grains have pure or high tilt angle component boundaries with adjacent grains, no clear slip bands can be observed because the high FCP rate across these grains fails to allow enough reversible dislocation slipping. Besides, in AA2297-T87 alloy, slip band formation depends heavily on the second-phase particles. From theoretical calculation and quantitative measurement prospective, the large size and density of unshearable T1 phases can retard dislocation shearing and motion, thereby suppressing the formation of slip bands.