Role of excess vacancies in the early stage solute clustering in aluminium alloys

Aluminium alloys play an important role in the sustainable metallurgy concept. On the way to design alloys with superior properties and more efficient processing routes, understanding the precipitation hardening in aluminium alloys on the mechanism level is essential as it is the most effective way to strengthen the aluminium. The precipitation process is started by solutionising and quenching the alloy, during which not only solutes are dissolved and preserved in a supersaturated state, but also excess vacancies are frozen-in. In this seminar talk we will discuss the role of these excess vacancies in the early stage clustering in the Al-Mg-Si alloys. The natural ageing clustering in this class of alloys is of particular significance due to its detrimental effect on the subsequent paint-bake hardening. Our results on the solute clustering in this alloy series can be outlined from three aspects, namely 1) how pre-ageing conditions suppresses subsequent natural ageing clustering, 2) how quenching after solutionising influences excess vacancies and natural ageing kinetics, 3) the contribution of excess vacancies to clustering at various ageing temperatures. We underline the importance of the interactions between solute clusters and vacancies in understanding the evolution of non-equilibrium excess vacancies as well as the early stage clustering kinetics.