Study of the early stages of clustering in Al–Mg–Si alloys using the electrical resistivity measurements

The natural ageing of Al–0.5%Mg–1%Si alloy at low temperatures, namely, −20, 0, RT and 50°C, is investigated through the use of the electrical resistivity measurements and positron annihilation spectroscopy. It was found that over extended periods of time, the resistivity increases linearly with the logarithm of time. More importantly, three clear stages of clustering were observed during natural ageing. The possible origin of these three distinct stages was briefly discussed. As well, the activation energy of clustering during the second stage was calculated using the cross-cut technique. The measured value was relatively close to the migration energies of vacancies and solute atoms (Mg/Si) which suggested an important role of them in the clustering process. Finally it was found that the solution treatment temperature does not have a significant effect on the mechanism of clustering.