Influence of Microalloying Elements on the Precipitation Behaviour of Aluminium Alloys

Al-Mg-Si alloys are widely used in cast, wrought and extruded form. A characteristic property of these alloys is the negative effect of natural pre-aging at room temperature on artificial aging. Minor additions of Sn suppress the adverse effect of room temperature aging due to controlled buffering of quenched-in excess vacancies at low temperatures. In this study we evaluate the buffering performance of Sn in the temperature range between 5 and 45 °C. This is investigated for two Sn-added AA6061 alloys with systematic variation in their Mg-, Si- and Cu-content, for comparison the natural aging kinetics of a Sn-free alloy is studied. In general a strong dependence of hardening kinetics on temperature and on chemical composition is observed. Results of aging kinetics are discussed in terms of common clustering theories and calculations of the temperature dependent trapping effect of Sn on excess vacancies.