Laser powder bed fusion of nano-CaB6 decorated 2024 aluminum alloy

Abstract The 2024 aluminum alloy (Al-Cu-Mg) is widely used in aerospace; however, due to its solidification-cracking tendency, its processability using laser powder bed fusion (LPBF) remains a critical issue. The addition of 2 wt% CaB6 nanoparticles induces a columnar-to-equiaxed transition (CET), resulting in an immediate improvement in LPBF processability. High-density (>99.5%) and crack-free specimens, with a homogeneous equiaxed microstructure and without preferred grain orientation, were obtained. The small average α-Al grain size of 0.91 ± 0.32 µm is attributed to the similar lattice constants of Al and CaB6 facilitating Al nucleation on CaB6 nanoparticles, resulting in a highly coherent Al/CaB6 interface. CaB6 nanoparticles act as heterogeneous nucleus and exert a pinning force on the grain boundaries, which reduces grain coarsening. The as-built specimens exhibit both high-yield strength (348 ± 16 MPa) and high-tensile strength (391 ± 22 MPa), combined with a high total elongation at break (12.6 ± 0.6%). The macro hardness amounts to 132 ± 4 HV5.