The effect of shear-resistant, plate-shaped precipitates on the work hardening of Al alloys: Towards a prediction of the strength-elongation correlation

The work hardening of a model Al-3Cu-0.05Sn (wt.%) alloy containing shear-resistant theta' (Al2Cu) precipitate plates was studied as a function of precipitate state. The mechanical response was monitored using both tension and tension-compression (Bauschinger) tests so that the isotropic and kinematic contributions to the work hardening could be separated. The undeformed and deformed structures were characterized using TEM. The kinematic hardening was modeled using the recent approach of Proudhon et al. [19], and good agreement was found for both the absolute magnitude and the strain evolution of the internal stress as a function of precipitate state. The isotropic hardening was modeled using a modified form of the Kocks-Mecking-Estrin approach, taking into account the contribution to the forest dislocation density from the plastic relaxation around the precipitate plates that accompanies the saturation in the internal stress during straining. In this way, the evolution of the isotropic and kinematic hardening during straining are coupled, and the dual role of the precipitates in contributing to both modes is emphasized. Finally a parametric analysis of the model is performed to identify the changes in microstructural parameters that will allow simultaneous increases in both yield strength and uniform elongation. It is suggested that increasing the precipitate number density of this system will achieve this end. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.