Achieving fully equiaxed grains with minor Sc addition of a novel Al-Li alloy fabricated by laser direct energy deposition

In this study, a novel Al-Li alloy with minor Sc addition was fabricated by laser directed energy deposition (LDED), resulting in a fully equiaxed grain structure. The precipitation behavior of primary Al₃Sc particles was studied based on transient nucleation theory, and the results showed that sufficient heterogeneous nuclei by primary Al₃Sc particles could preferentially form at initial solidification stage and induce into equiaxed grains. Besides, a large number of acicular T₁ (Al₂CuLi) phases and spherical Al₃Sc phases, as well as rod-shaped T_B (Al₇Cu₄Li) phases and quasicrystalline T₂ (Al₆CuLi₃) phases, were distributed in as-built alloy that served as primary strengthening phases by thermal cycling. However, the specific nucleation behavior of α-Al grains on primary Al₃Sc particles and subsequent growth behavior during rapid solidification need to be further investigated.