Abstract
In-situ deformation experiments in the high-voltage electron microscope have been performed on the precipitation-hardened alloy Al–1 at.% Ag, isothermally aged at 413 K for different times, in order to explain a maximum of unknown origin in the critical resolved shear stress during ageing. The dislocations move in a jerky manner. In the stable positions, they bow out between precipitates. The spectrum of obstacle distances h (l) and the mean obstacle distance 1 along the dislocation line as well as the curvature of the dislocation segments have been evaluated from the electron micrographs. The obstacle distances are longer by a factor of about five than those determined from the size and density of the precipitates. The dislocation curvature corresponds to a stress which is higher than the macroscopic yield stress. Data in the literature suggest that there is a re-solution process between ε and η particles in the alloy. The flow stress is assumed to be mainly controlled by the η precipitates. Their high strength cannot solely be due to stacking-fault hardening. Elastic interactions between the particles and dislocations and/or order hardening may additionally contribute to the flow stress.
