Study on microstructure evolution and aging precipitation behavior of a novel Al-Li alloy fabricated by laser rapid melting

For Sc-containing Al-Li alloys, Al3Sc precipitates exhibited inhomogeneous distribution due to limited solid solubility, segregation and sluggish diffusion of Sc. Laser rapid melting (LRM) with its merit of increasing the solubility of alloying elements during solidification represents a pivotal technique for exploring new alloy compositions. In this study, microstructure evolution and aging precipitation behavior of a novel Al-Li-Cu-Mg-Ag-Sc alloy fabricated by LRM were investigated during a systematically optimized T6 heat treatment. No primary Al3Sc particles were formed during the rapid solidification, but coherent Al3Sc nanoparticles were precipitated in the subsequent cooling process. Maximum hardness of 202 HV was achieved after aging at 175 °C/18 h due to combined precipitation strengthening of the Al3Sc, δ', Al3(Li, Sc) and T1 phases. Coherent Al3Sc was concerned with a sequence of atomic displacement modulations that led to varying degrees of {002}Al planar collapse, while interfacial dislocations were emitted from the interface of Al3Sc with coherency lost. The existing Al3Sc phases were available to be acted as nucleation sites for δ′ and T1 to form composite phases. These results can provide indispensable information for compositional design of novel Al-Li alloy specifically for laser additive manufacturing.