LAUSR

Abstract The natural ageing effect on artificial ageing kinetics of Al-Zn-Mg alloy has been studied using small angle X-ray scattering, transmission electron microscopy and mechanical testing methods. The results have demonstrated that with 72 hours natural ageing treatment prior to pre-ageing process can inhibit following natural ageing effect. Samples with direct pre-ageing treatment after quenching from solution temperature exhibit significant natural ageing effect subsequently. The strengthening effect is mainly attributed to the formation of fine GP-zones with particle sizes of less than 1 nm. The microstructures characterization has shown that these GP-zones may transform to precursor of η′ precipitate during pre-ageing process if their size reached a critical size. These precursor of η′ precipitate with the size of ∼1 nm–∼1.2 nm are stable at room temperature.