In situ small-angle scattering study of the precipitation kinetics in an Al–Zr–Sc alloy

A time-resolved small-angle X-ray scattering (SAXS) study was carried out to investigate the precipitation kinetics of L12 Al3(Zr, Sc) precipitates in aluminium at temperatures ranging between 400 and 475 °C. It is shown that the chemical heterogeneity of the precipitates, which consist of a Sc-rich core and a Zr-rich shell, results in a characteristic SAXS signal, which can be fitted by a three-phase model to extract the chemical and morphological features of the precipitate size distribution. The experimental results show a strong effect of the heating rate on the precipitation kinetics, and a precipitate density strikingly constant with time in the investigated range. These results are discussed in view of the mechanisms proposed in the existing literature for the formation of the core–shell structure of these precipitates.