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 T-2 phase gathered around grain boundary and T-B phase in grain interior. Diffraction patterns of quasi-crystalline T-2 phase show two-fold, three-fold and five-fold symmetry, respectively. Under condition of thermal cycling, T-2 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 degrees C for 1.5 h, delta' phase, T-1 phase and T-B phase are completely dissolved in matrix, while quasi-crystalline T-2 phase transforms into orthorhombic O phase. The size of O phase is similar to that of T-2, with length of about 400 nm and rougher surface.