Saxs and tem study of the kinetics of phase separation in Al-Zn

Kinetics of phase separation and coarsening in Al-22 at.% Zn-0.1 at. % Mg, from very early to very late annealing times, has been studied by correlating the time evolution of the small-angle X-ray scattering spectrum and the microstructure, as revealed by transmission electron microscopy. Three kinetic regimes were recognized. The dominant coarsening mechanisms were interpreted as arising from cluster coagulation at early times and single atom diffusion at late times. The intermediate times probably combined both. The microstructure consisted of interconnected spherical clusters at early times and regularly spaced platelets at late times; with a mixture of both during the transition period. At later annealing times, the intensity spectra exhibited a “shoulder” whose appearance was associated with the change of morphology. The intensity spectra from different times could all be made to coincide on one curve through appropriate scaling, provided the microstructure was not changing during that time period. Simple analytical forms described the shape of the scaled intensity curves.