Effects of Al3Sc particle size and precipitate-free zones on fatigue behavior and dislocation structure of an aged Al–Mg–Sc alloy

Al–Mg–Sc alloy polycrystals have been cyclically deformed at room temperature under constant stress amplitudes. Cyclic softening after initial hardening is found in specimens with small particles of 4 nm, but no cyclic softening takes place in specimens with large particles of 11 nm. Transmission electron microscopy observations reveal that dislocations are uniformly distributed under all applied stress amplitudes in the specimens containing large particles, whereas clearly developed slip bands are formed in the cyclically softened specimens bearing small particles. Two-step aging causes a decrease in the width of precipitate-free zones in the large-particle specimen, resulting in the improvement of fatigue life.