Study of the precipitation kinetics in an Al–8.9 at.% Li alloy using small-angle neutron scattering

Abstract

The growth of δ' precipitates in an Al–8.9 at.% Li alloy was studied by small angle neutron scattering experiments in the temperature range from 363 to 483 K. The radius, number density and volume fraction of the precipitates and the concentration of the solute in the matrix were determined as functions of the ageing temperature and time. All the parameters determined, except those corresponding to short ageing at 363 K, follow the predictions of the coarsening theories. From the increase in the radius of the precipitates, the decrease in their number density and the decrease in the solute concentration in the matrix versus ageing time, the corresponding kinetic constants were determined for the different ageing temperatures. The three sets of kinetic constants give within errors the same energy for diffusion, having a mean value of 1.24 ± 0.03 eV. The δ'-α solvus line was determined and agrees well with that available in the literature and theoretical calculations. The diffusion constant and the δ'-α interfacial energy are determined for different models of coarsening. The data at 363 K are interpreted by empirical equations used previously to describe the short time ageing at higher temperatures.