Hierarchical MgAl₂O₄/Al₃Ti nucleating agents induce full equiaxed grains in laser-powder-bed-fused Al alloys

Laser powder bed fusion (LPBF) provides high design freedom for high-strength aluminum alloys in aerospace and automotive industries. However, the rapid solidification of LPBF results in a critical microstructural challenge in aluminum alloys: coarse columnar grains with anisotropy and cracking. In this work, we employ the synergistic effect of magnesium and titanium elements in aluminum alloys for building self-assembled MgAl₂O₄/Al₃Ti hierarchical architectures as a highly efficient nucleation agent. In-situ MgAl₂O₄ nanoparticles offer coherent interfaces (lattice mismatch: 0.05 %) for the nucleation of L1₂-structured Al₃Ti phase, facilitating the formation of fully equiaxed grains with random orientations in aluminum alloys. Aberration-corrected transmission electron microscopy demonstrates atomic-scale coherence at MgAl₂O₄/Al₃Ti interfaces, confirming MgAl₂O₄ as effective nucleation substrates for Al₃Ti phase. Our study provides a new microstructure-design strategy for LPBF, achieving aluminum alloys with fully equiaxed grains.