Study of icosahedral quasi-crystalline phase T₂-Al₆CuLi₃ and transformation in 2A97 Al-Li alloy fabricated by laser additive manufacturing

Precipitated phases of 2A97 Al-Li alloy fabricated by laser additive manufacturing with thermal input are mainly composed of quasicrystal T₂ phase gathered around grain boundary and T_B phase in grain interior. Diffraction patterns of quasi-crystalline T₂ phase show two-fold, three-fold and five-fold symmetry, respectively. Under condition of thermal cycling, T₂ phase transforms into a face-centered cubic Y phase with a lattice constant of 2 nm. Y phase can grow into twins, and the twin plane is (1 1 1). After solution treatment at 515 °C for 1.5 h, δ' phase, T₁ phase and T_B phase are completely dissolved in matrix, while quasi-crystalline T₂ phase transforms into orthorhombic O phase. The size of O phase is similar to that of T₂, with length of about 400 nm and rougher surface.