Analysis of thermoelectric power measurements in the study of precipitation kinetics in 3003 Al alloy

Multiphase precipitation kinetics for a 3003 aluminum alloy, pointed out in our previous work and obtained under different microstructural conditions by thermoelectric power measurements, is now modeled under the light of the theory of reaction rates. Our multiphase model encompasses the precipitation kernels of Johnson-Mehl-Avrami (JMA) and of Fujita-Damask (FD), which adequately reproduce the experimental kinetics. The JMA kernel generates almost constant values for the exponent n. These values are less than those in temperature ranges where the log of the rate constant k grows linearly with the inverse of the temperature. The FD kernel provides an idea of the average critical size of the phase which is formed. Our multiphase results are compared with those obtained from the traditional monophase considerations rendering evident important differences between both models. The total kinetics is deconvoluted, allowing us to characterize the different metastable and stable phases formed according to the different microstructural conditions. The activation energy for kinetics in "as-cast" samples behaves differently from that obtained from the microstructures in homogenized and homogenized-strain samples. The activation energy for each of these cases is reported.