Quantitative description of the T₁ morphology and strengthening mechanisms in an age-hardenable Al-Li-Cu alloy

In the Al-Cu-Li system, the main strengthening precipitate is the T₁ phase (Al₂CuLi). In order to understand the strengthening related to the formation of this phase, we first present an investigation of the morphology of the T₁ phase in an AA2198 alloy using Transmission Electron Microscopy (TEM) and Differential Scanning Calorimetry (DSC) in relation with the evolution of micro-hardness. In parallel, we present an investigation of the interaction between T₁ precipitates and dislocations using High Angle Annular Dark Field (HAADF) imaging in an atomic resolution Scanning Transmission Electron Microscope (STEM). The atomic scale imaging of precipitates makes it possible to quantify the density of shearing events, which turns out to be insufficient to account for the imposed plastic strain. We discuss the implications of this result in terms of precipitate-dislocation interactions.