Role of vacancy-solute complex in the initial rapid age hardening in an Al-Cu-Mg alloy

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 vacancies are bound to Mg atoms rather than Cu atoms initially and the vacancy-Mg complexes easily migrate to vacancy sinks at 150°C. Vacancy-Mg-Cu complexes form during the initial 1 min aging at vacancy sinks, meanwhile vacancy density decreases rapidly. These results support that the dislocation-solute interaction is the origin of the initial rapid hardening.