Segregation of Zinc to Vacancy Sinks in Aluminum

During air cooling from a high-temperature anneal, vacancy currents were observed to cause zinc to segregate around vacancy precipitate cavities in aluminum. From the vacancy and zinc impurity currents directly measured in this experiment, a maximum value of the ratio of vacancy jump frequencies away from and around a zinc impurity atom in aluminum is determined. This limiting ratio suggests a small attractive interaction between a vacancy and a zinc impurity and/or an increase in the jump frequency of aluminum atoms around the undersized zinc atom. The segregation that would be produced around grain-boundary vacancy sinks during quenching and irradiation was computed from the experimental values of the ratio of the vacancy current and the vacancy-generated impurity current measured in this and other experiments. It was found that moderate and very large changes in grain-boundary solute concentration could be expected during quenching and irradiation, respectively.