Enhanced printability and strength of unweldable AA2024-based nanocomposites fabricated by laser powder bed fusion via nano-TiC-induced grain refinement

Abstract

The formation of undesirable coarse columnar grains and periodic hot cracks has been a long-standing issue in the additive manufacturing (AM) of unweldable high-strength aluminum alloys and their nanocomposites. Herein, the LPBF-printability of AA2024-based nanocomposites is improved by TiC-induced in-situ reinforcement and nanoparticle-enabled grain refinement during laser powder bed fusion (LPBF). The TiC-triggered in-situ reaction during LPBF overcomes the poisoning of the TiC grain refiner that occurs during conventional solidification. It not only results in fine equiaxed grains with a minimum average size of ∼1.6 μm but also suppresses hot crack formation. Powerful L12-Al3Ti nucleants are incorporated in-situ into AA2024 through TiC nanoparticle addition during LPBF, promoting the heterogeneous nucleation of α-Al. Moreover, the growth restriction effect induced by residual TiC nanoparticles and lamellar Al4C3 nanoparticles through pinning behavior along grain boundaries also contributes to grain refinement. Furthermore, these particles serve as effective reinforcement particles as well as grain refiners. The as-built AA2024-based nanocomposites tailored by nano-TiC show a maximum ultimate tensile strength (UTS) of ∼388 MPa, a yield strength (YS) of ∼332 MPa and an elongation (El) of ∼10.2%. After T6 heat treatment, the nanocomposites exhibit an outstanding UTS of ∼507 MPa, a YS of ∼456 MPa and an El of ∼6.6%. This nano-TiC-induced microstructural control method provides new insights into successful AM of hot-crack-sensitive high-strength aluminum alloys and their composites.