Vacancy-solute aggregates in Al-Cu-Mg alloys studied by positron annihilation techniques

Vacancy-solute aggregates formed in the alloy Al-Cu (4.38 wt %)-Mg (1.62 wt %) were studied by two different positron annihilation techniques (lifetime spectroscopy and two-detectors Doppler broadening spectroscopy) and by differential scanning calorimetry (DSC). The results show that the concentration of Cu in the environment of a vacancy increases when the temperature of aging is raised from 20 to 60 ^∘{}C. Structural transformations, which produce a reordering of the chemical species in contact with vacancies and an energetic stabilization of the solute aggregates, are observed to occur at room temperature after aging at 180 ^∘{}C through effects on the kinetics of the average positron lifetime as well as on DSC thermograms.