The Role Of Quenched-in Vacancies For The Decomposition Of Aluminium Alloys

摘要

The very early stages of decomposition during room temperature storage, i.e. just a few minutes after quenching, are investigated by positron annihilation lifetime spectroscopy for both an AlMgSi alloy and an AlCuMg alloy. It turns out that by freezing the decomposition kinetics during measurements we can detect vacancy-solute atom pairs. The formation of larger solute clusters with structural vacancies is seen by an increase of the mean positron lifetime in the course of storagernat room temperature (RT). Earlier findings concerning aging at RT were unable to discover this effect. The detected changes are interpreted in terms of cluster formation. Thus we show that positron annihilation spectroscopy (PAS) is one of the very few methods to access early stages of decomposition in metallic alloys. Moreover, the lower limit of the concentration of quenched-in vacancy-like defects is calculated to be at least 2 × 10~(-5) per atom.