Muon Spin Relaxation Study of Solute–Vacancy Interactions During Natural Aging of Al-Mg-Si-Cu Alloys

Muon spin relaxation has the unique ability to detect very low concentrations of vacancies and vacancy–solute complexes in solids. In this work, we investigate quaternary Al-Mg-Si-Cu alloys and show that after quenching to room temperature from 848 K (575 °C), vacancies gradually become incorporated into clusters in the Al matrix. The total amount of vacancies in the material increases as small vacancy-rich clusters are formed, which is the opposite of the behavior in Cu-free Al-Mg-Si alloys.