Fatigue softening of AlMg single crystals

Abstract

The fatigue softening of Al-0.7 at.% Mg single crystals was studied by cyclic deformation at a constant plastic shear strain amplitude of ±0.01 of specimens prestrained in tension. The changes in the defect microstructure occuring during fatigue softening were studied by transmission electron microscopy. The results show that the saturation flow stress in independent of the amount of prestrain in tension. The cell size along the Burgers vector on the primary slip plane at the saturation stage is almost the same after either fatigue hardening or fatigue softening. The cell walls containing tangles of primary and secondary dislocations formed during prestraining in tension change into a regular array of primary and secondary dislocations after fatigue softening. The fatigue softening occurs by the dissociation of dislocation barriers such as Cottrell-Lomer and Hirth locks and the climb of dislocations enhanced by the point defects created during fatigue deformation. The defect microstructure and saturation stress are dependent only on the plastic shear strain amplitude and independent of the amount of prestrain before cyclic deformation of Al-0.7 at.%Mg single crystals.