The formation of nanoscale and sub-nanoscale solute aggregates (clusters, Guinier-Preston zones, precipitates) in Al-2.1Zn-1.5at%Mg was monitored by using a combination of experimental techniques with the aim of correlating the properties of the aggregates with their thermal history. The choice of heat-treatments was guided by the results of mechanical and calorimetric characterizations, supported by transmission electron microscopy for the identification of the morphology of the aggregates. Positron annihilation spectroscopy (using coincidence Doppler broadening and lifetime spectroscopy) was used to determine the local chemistry in the proximity of open-volume defects. The geometrical parameters of the distribution (size, volume fraction, numerical density of the solute aggregates) were obtained by small-angle X-ray scattering. The results of the investigation provided new information with regard to 2 families of vacancy-rich clusters formed by quenching, Guinier-Preston zones formed at 95C after room-temperature pre-aging, the growth of η’ and η phases at 150C and solute clusters formed at room-temperature under conditions of secondary aging after preliminary heating at 150C.

Hardening Nanostructures in an AlZnMg Alloy. A.Dupasquier, R.Ferragut, M.M.Iglesias, M.Massazza, G.Riontino, P.Mengucci, G.Barucca, C.E.Macchi, A.Somoza: Philosophical Magazine, 2007, 87[22], 3297-323