Fatigue behavior and microstructure of an Al-Mg-Sc alloy at an elevated temperature

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Al-Mg-Sc alloy polycrystals bearing Al3Sc particles with different sizes, i.e. 4, 6 and 11 nm in diameter, have been cyclically deformed at 423 K under constant plastic-strain amplitudes, and the microstructural evolution has been investigated in relation to the stress-strain response. Cyclic softening after initial hardening is found in specimens with small particles of 4 and 6 nm, but no cyclic softening takes place in specimens with larger particles of 11 nm. These features of cyclic deformation behavior are similar to the results previously obtained at room temperature. Transmission electron microscopy observations reveal that dislocations are uniformly distributed under all applied strain amplitudes in the specimens containing large particles of 11 nm, whereas slip bands are formed in the cyclically softened specimens bearing smaller particles. The cyclic softening is explained by a loss of particle strength through particle shearing within strongly strained slip bands. The 6 and 11 nm Al3Sc particles have a stronger retardation effect on the formation of fatigue-induced stable dislocation structure than 4 nm particles at 423 K. © 2010 IOP Publishing Ltd.