Precipitation and Dissolution of Intermetallic Phases During Recrystallization in Nanostructured Lightweight Alloys

Alloys subjected to severe plastic deformation result in highly distorted nanostructured materials characterized by significant disorder. This disorder is expressed through residual stresses, elevated vacancy concentrations, high dislocation densities, a large grain-boundary to crystallite bulk volume ratio, and substantial crystallographic site disorder in intermetallic compounds, which can even lead to their dissolution. Their heat treatment at increasing temperatures typically leads to recovery, recrystallization, and grain growth. The stored energy driving recrystallization expels significant concentrations of vacancies into the crystal lattices, expediting diffusion and thus the precipitation of intermetallic phases, which may transform or dissolve again at higher temperatures. Here, we present synchrotron micro-beam high-energy X-ray diffraction studies of lightweight alloys, such as Mg-AZ31 and Al-Cu-Li-Mg alloys, revealing in real time the stress relaxation, precipitation kinetics during recrystallization, vacancy concentrations, grain size, and dislocation densities. In particular, the recrystallization process can be employed to tune the microstructure of these materials.