Quantification of precipitate evolution in cast Al–Li alloys containing Cu and Mg additions using small-angle X-ray scattering

In this work, the evolution of precipitates which formed under artificial aging in three kinds of cast Al–Li alloys was described by combining small-angle X-ray scattering (SAXS), transmission electron microscope (TEM) and differential Scanning Calorimeter (DSC). By analyzing SAXS data, the size, axial ratio and volume fraction of precipitates were characterized, and the effects of Cu and Mg on the evolution of δ′ and T1 particles under isothermal aging were quantitatively studied. The result shows that the precipitation of T1 competes with δ′ phase, leading to a significant increase in the volume fraction of precipitates in Cu-containing alloys. And the addition of Mg (0.5%) in Al–Li–Cu alloy induced the nucleation process of T1 phase, reduced the thickness and increased the number density of particles, and slightly increased the total volume fraction of precipitate, which was consistent with the results of TEM and DSC studies. Based on the revised formula, the relationship between the morphology of T1 particles and their shear stress on dislocations was described, thereby elucidating that magnesium atoms affect the mechanical properties of the alloy by regulating the morphology of T1 particles.