Simultaneous Dissolution and Coarsening of δ′ Precipitates in Al–Li Alloys During DSC Experiments

In situ synchrotron radiation small-angle and 100 Bragg scattering experiments have been performed to examine the microstructural change of preaged Al–Li alloys during heating at a constant rate. When heating an Al-7.9 at.% Li sample preaged at 423 K, the average radius decreases first and then increases at higher temperatures. The decrease in the radius is hardly observable for Al-11.8 at.% Li aged at 423 K and Al-7.9 at.% Li aged at 333 K. The difference in the change of average precipitate size is explained on the basis of the kinetics by combining isothermal dissolution and coarsening data. The present results suggest that a coarsening during differential scanning calorimetry experiments is rather common, and it should be considered in more detail when analysing such experiments.