Li clustering in Al-Li alloys studied using positrons

The behaviour of two Al-Li dilute alloys having two different Li contents (1.7 and 3.7 at.%Li) has been studied using positron annihilation. The lifetime value is about 20 ps higher than that measured for pure Al and is independent of the Li content. When the specimens are cold rolled the lifetime increases to a value that is lower than the one currently associated with dislocations in Al and does not depend on the Li concentration. After isochronal annealing the lifetime achieves the initial value tau =185 ps. The results are interpreted in terms of Li clustering.