Effect of plastic deformation on precipitation in Al-30 wt.% Zn alloy aged at 200 °C

Abstract

The electron microscopic investigation of an Al-30 wt.% Zn alloy reveals that the plastic deformation of quenched samples substantionally modifies the phase transformation processes examined in the alloy aged at 200°C. Whereas the growth kinetics of metastable precipitates and associated solute diffusion are unaffected by cold rolling the alloy specimens from 9% up to 97·5% reduction in thickness, the rate of all observed transformations is enhanced considerably by prior plastic deformation. A corresponding increase of stored strain energy within the lattice provides namely an additional driving force for the establishment of a new precipitate/matrix interface of higher surface energy on the transformation of a metastable precipitate into a more stable one. The sizes of transforming transition precipitates consequently diminish with an increase of cold work and the respective transformations are thus accelerated.