Deformation-assisted precipitation and segregation in Al-Li alloy AA2099

Abstract

In this work, the chemo-mechanical evolution of microstructural features as a function of strain during room temperature severe plastic deformation of an Al-Li alloy has been investigated. Detailed microscopic analysis of the high-pressure torsion (HPT) processed AA2099 alloy reveals several key insights. At lower strain levels of HPT deformation, we observe the segregation of Mg solutes and the formation of Mg-Zn-rich nanoclusters at the grain boundaries to reduce the energy of the non-equilibrium boundaries. The enhanced diffusion of solutes at room temperature is aided by the excess defect density. For the first time, Li-decorated dislocation loops are observed within the matrix, where Li segregation reduces the elastic strain energy of the loops. A few Cu-Zn-rich precipitates nucleate at triple junctions. As strain reaches steady-state, Mg-Zn-rich and Li-rich clusters dissolve, and Mg atoms redistribute from the grain boundaries, while most triple junctions become decorated with Cu-Zn-rich precipitates. These findings provide valuable guidance for the strategic microstructural optimization of Al-Li alloys in advanced applications.