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

The low-cycle fatigue behaviour 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 x 10(-4) to 5.0 x 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 x 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. (C) 2004 Elsevier B.V. All rights reserved.