Deformation of fine-grained aluminium alloys

Abstract

AbstractAbstractThe deformation of an ultrafine-grained aluminium alloy has been examined in tension and torsion. At grain sizes below about 3 μm the alloy exhibits inhomogeneous yielding but this is absent at larger grain sizes. If the lower yield strength values are plotted versus grain size the strengths are inversely dependent on grain size whereas the usual plot versus d−½ is non-linear and shows an enhanced strength at the finer grain sizes. However, if the inhomogeneous yielding region is avoided by extrapolating the work-hardening portion of the curve back to the elastic line, all the data can be well represented by the Hall–Petch relationship. Torsion tests, which allow the investigation of a large strain range, show that. the gredient of the grain size plots decreases slowly wIth strain but that the grain boundaries remain effective barriers to flow at strains up to at least 1.0. The deformation behaviour does not appear to agree with the current models for the influence of grain size on the flow stress but can be understood qualitatively in terms of the different dislocations structures generated at various grain sizes.