Effect of Sn and In on the Natural Ageing Kinetics of Al-Mg-Si Alloys

Abstract

The deleterious effect of natural ageing (NA) on subsequent artificial ageing (AA) of Al-Mg-Si alloys can be markedly reduced by adding small amounts of Sn owing to the strong interaction between Sn atoms and excess vacancies. The retarding effect of Sn on clustering after quenching and during NA was verified in this study. The largest effect was found in a solute-lean Al-Mg-Si alloy containing 70 ppm Sn and solutionised at 570 °C. Employing the same strategy, the delayed clustering kinetics was also observed in alloys in which Sn was replaced with In. Based on the data obtained from positron annihilation lifetime, hardness and electrical resistivity experiments，we introduce some concepts describing the mechanisms of NA cluster formation in the presence of Sn (In) based on vacancy-solutes interactions.