Irreversible decomposition of an AlLi single crystal has been studied by x-ray photon correlation spectroscopy. The precipitate coarsening follows a universal behavior, as measured by the time-resolved average scattering. Using coherent scattering, two-time correlation functions have been measured. The time evolution of the speckle pattern gives new insight into the process of unmixing; at least two regimes govern this evaporation-condensation coarsening process. One is related to the overall arrangement of precipitates, and the characteristic time is linear with annealing time. The other is related to the motion of interfaces and is related to Porod's law.