Transformation processes in deformed Al-30 wt.% Zn alloy containing metastable precipitates

Abstract

The Al-30wt.%Zn alloy containing metastable α′_R or α′ precipitates was cold rolled to investigate the effect of plastic deformation on transformation processes during the subsequent ageing at 200 °C. Transmission electron microscopy and X-ray diffraction studies proved that the deformation leads to the rapid decomposition of deformed α′_R and α′ precipitates and enhances also the decomposition of α′ precipitates formed from α′_R to α′ transformation. The deformation does not, however, change the growth rate of α′ particles. It leads, therefore, to the decrease of critical sizes of α′ particles for the α′ to β transformation. The increasing degree of deformation enhances the density of nucleation sites for the β formation on α/α′ interfaces and leads to the decrease in sizes of stable β precipitates. The acceleration of transformation processes is associated with the partial relaxation of stresses introduced by the applied deformation.