Natural Aging in Al Mg Si Alloys A Process of Unexpected Complexity

The natural ageing behaviour of pure ternary Al Mg Si alloys is investigated by measuring hardness, electrical resistivity and positron lifetime, as well as carrying out thermal analysis and atom probe microscopy. It is found that several distinct temporal stages of natural ageing can be distinguished in which one of these quantities shows a characteristic behaviour and that these times coincide for many of these measurements. The rate of change in the measured data is correlated with proposed solute dynamics during natural ageing for both ageing that takes place prior to artificial ageing natural pre ageing and post artificial underageing natural secondary ageing heat treatments. Controlling factors for solute dynamics are discussed