A POSITRON-ANNIHILATION STUDY OF THE FORMATION AND DISSOLUTION OF L1(2) PRECIPITATES IN AL-LI ALLOYS

The formation and dissolution of delta' precipitates has been followed by positron annihilation spectroscopy in two Al-Li alloys (Al-9.9at.% Li and Al-8.6 at.%Li-0.04at.%Zr). Lifetime measurements have been perf ormed by annealing the samples from the as-quenched state to 750 K, wh ich is well above the dissolution temperature for the delta-phase Al3L i. The results suggest that small delta'-like regions are present in t he as-quenched state, and that they dissolve at around 430 K, in agree ment with previous results in the literature. The technique has proved to be very sensitive to the growth and dissolution of delta' precipit ates owing to the high positron affinity to Li in an Al matrix.