• Yang, Z.; Jiang, X.; Zhang, X.; Liu, M.; Liang, Z.; Levraz, D.; Banhart, J.: Natural ageing clustering under different quenching conditions in an Al-Mg-Si alloy. Scripta Materialia 190 (2021), p. 179-182

10.1016/j.scriptamat.2020.08.046

Abstract:
During quenching of aluminium alloys from the solutionising temperature vacancies are partially con- served as excess vacancies, partially lost to vacancy sinks, the exact fractions depending on the cooling rate. Positron lifetime measurements in samples from interrupted quenching experiments reveal that va- cancies are lost during cooling down to 200 °C, after which solute atoms start to form clusters down to 20 °C. Slow cooling leads to 1 to 2 orders of magnitude lower excess vacancies than fast cooling. Since quenched-in vacancies are crucial for natural ageing (NA) in Al-Mg-Si alloys it is surprising to find just small differences between the NA hardening kinetics after different quenches. Specifically, hardening rates differ only in the initial stage ( < 100 min), after which they are almost identical for NA up to ~1 year. This suggests that interactions between vacancies and early-stage solute clusters help equalising the free vacancy fractions in differently quenched samples.