Experimental and modelling assessment of precipitation kinetics in an Al-Li-Mg alloy

The precipitation behaviour in an Al-5 wt.% Mg-1.8 wt.% Li alloy has been systematically investigated for both isothermal and non-isothermal heat treatments, using atom probe tomography, transmission electron microscopy and in situ small-angle X-ray scattering. In the investigated temperature range, the δ′ phase is shown to form, with a Mg content similar to that of the alloy, and a Li content of 18.5 at.%. The quantitative data on isothermal and non-isothermal kinetics from the in situ experiments are compared to the outcome of a precipitation class model adapted to the case of high volume fractions. The model parameters suggest that the main effect of Mg on the precipitation of the δ′ phase in Al is to lower the solubility of Li in the α-Al solid solution, with little effect on the interfacial energy of the precipitates or on the Li diffusivity in Al.