We have investigated the origin of the initial rapid hardening of an Al-1.3
at .% Mg-1.7 at .% Cu alloy by coincidence Doppler broadening of positron
annihilation radiation and positron lifetime spectroscopy. Quenched-in vaca
ncies are bound to Mg atoms rather than Cu atoms initially and the vacancy-
Mg complexes easily migrate to vacancy sinks at 150 degreesC. Vacancy-Mg-Cu
complexes form during the initial 1 min aging at vacancy sinks, meanwhile
vacancy density decreases rapidly. These results support that the dislocati
on-solute interaction is the origin of the initial rapid hardening. (C) 200
1 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserv
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