Resolving lithium distribution in the T₁ phase of Al-Cu-Li alloys via crystallography-guided atom probe tomography

The T₁ phase (Al₂CuLi) is the primary strengthening precipitate in advanced Al–Cu–Li alloys. However, directly determining the site-specific distribution of Li within its atomic lattice has remained a long-standing challenge. Here, we introduce a crystallography-guided methodology that exploits the fixed angular relationships between T₁ plates on different {111}_Al habit planes. Virtual rotation of Atom probe tomography (APT) reconstruction to satisfy these constraints enables identification of the Al 〈110〉 and 〈112〉 zone axis which are characteristic observation directions for the T₁ phase. The Li distribution extracted along these specific orientations shows excellent agreement with aberration-corrected STEM imaging and density functional theory (DFT) calculations, providing robust validation of our approach. This work establishes a broadly applicable paradigm for the correlative characterization of complex precipitates, particularly those containing ultra-light elements.