The effect of thermal processing variables on the isothermal clustering appears to occur during the quenching process, which is found to have a significant bearing on the growth of zones during early aging. The precipitation of intermediate precipitate eta prime is found to be controlled by vacancy concentration as well as supersaturation. The data obtained have been examined in the light of earlier work related to precipitate-nucleation, precipitate-free-zone, clustering kinetics, and quenched-in vacancies.