Low-cycle fatigue behavior and dislocation structure of an Al–Mg–Sc alloy

The low-cycle fatigue behavior of an Al–Mg–Sc alloy containing coherent Al3Sc particles with average diameters 4 and 11 nm was examined under constant plastic-strain amplitudes in the range of 1.0 × 10−4 to 5.0 × 10−3. Although the coherent Al3Sc particles are shearable, no cyclic softening was observed in specimens with large particles of 11 nm. Specimens with small particles of 4 nm showed cyclic softening at plastic-strain amplitudes higher than 1.0 × 10−3. In the large-particle specimens, dislocations were uniformly distributed under all applied plastic-strain amplitudes, whereas the small-particle specimens, in which the cyclic softening occurred, exhibited clearly developed slip bands. The cyclic softening can be explained by a loss of particle strength through particle redissolution within strongly strained slip bands.