ON THE KINETICS OF DISCONTINUOUS PRECIPITATION IN AN AL-14.6 AT PERCENT ZN ALLOY

Abstract

The influence of the continuous precipitation on the discontinuous precipitation in an Al-14.6 at.% Zn alloy has been studied using optical microscopy, resistivity measurement, high angle X-ray study, small angle X-ray study, and transmission electron microscopy. Results showed that a considerable amount of decomposition (up to 9 approximately 15 vol.%) takes place in the matrix through the prior continuous precipitation before the onset of the discontinuous precipitation at the grain boundary. The growth rate of the cellular structure due to the discontinuous precipitation appears not to be directly related with the available chemical free energy, nor with the available total free energy, but to be directly related with the strain energy associated with the prior continuous precipitation of coherent G.P. zones.