Kinetics of particle growth and particle composition of a commercial Al-Li alloy by means of small-angle scattering

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Abstract
Extending previous work done on a similar alloy, small-angle X-ray scattering measurements are reported for a commercial Al-Cu-Li alloy (2–68% Cu and 1–88% Li by weight). Data have been analysed by means of an ellipsoidal model of precipitate particles using a method previously proposed by some of us which, incorporating interparticle interference effects, reproduces the fuli scattering intensities of the samples studied. Particie dimensions obtained from the fit indicate that the Lifshitz-Slyozov coarsening mechanism holds for ageing at higher temperatures and longer times. The activation energy for volume diffusivity obtained is similar to that of pure binary alloys. The scattering-curve fitting parameters include the volume fractions of the δ-phase which decrease as expected with increasing temperature. The scattering contrast between δ and the matrix is observed to increase with temperature. On the basis of these observations, it would appear that the lithium concentrations in both the matrix and the precipitate increase with increasing temperature.