Low temperature post-precipitation after precipitation of β′ and β phases in Al-12 wt.% Mg alloy

TEM observation confirms the presence of Guinier-Preston (GP) zones in close association with particles of P-phase after natural ageing at room temperature of Al-12 wt.% Mg alloy which has been preliminary homogenised, quenched and aged at 250 degrees C. Each time the sample is sufficiently matured at ambient temperature, after a first pre-precipitation (formation of GP zones) or precipitation (formation of beta' or beta phases), new zones form without the presence of the quenched-in vacancies. Since quenched-in vacancies, obtained after a rapid quench in water, have greatly increased the rate of beta' and beta phases formation and have reached their equilibrium concentration, the GP zones formation occurs without their presence. These results have been obtained preliminary by dilatometric and calorimetric analysis, which confirm their importance and their complimentarily in the study of the ageing processes in different alloys due to their sensitivity to various precipitation stages. (c) 2007 Elsevier B.V. All rights reserved.