In-situ amorphous/crystalline heterostructure enables high strength and ductility in laser powder bed fused AlMgErZr alloys via 316L functional alloying

Additive manufacturing of high-strength aluminum alloys faces two fundamental limitations: crack susceptibility and strength-ductility trade-offs. To address these challenges, we propose an in-situ alloy design strategy to spatially modulate the microstructure in AlMgErZr alloys during laser powder bed fusion (LPBF) by introducing 316L stainless steel as a functional additive. With increasing 316L content, solute-induced constitutional undercooling promotes a transition in grain morphology from columnar to cellular/dendritic, resulting in hierarchical heterostructure. At the optimal 2.5 wt%316L addition, the α-Al matrix is partitioned by submicron-to-micron cellular network consisting of amorphous Al-Fe-Ni nanoprecipitates, coherent L1₂-Al₃(Er, Zr) and incoherent Mg₂Si precipitates. This design creates a multi-element effect that promotes amorphous phase formation through strongly negative Al–Fe–Ni mixing enthalpies as the thermodynamic driver, combined with enhanced configurational entropy and atomic size mismatch from large-radius (Er, Zr, Sc) and solid-solution (Mg, Cr) elements. The cellular network serves as a reinforcement carrier and coordinates plastic deformation to homogenize strain, thereby enabling multiple strengthening mechanisms: amorphous precipitates enable interface-mediated dislocation annihilation and Orowan strengthening, while L1₂ nanoprecipitates contribute through ordering and anti-phase boundary effects. Additionally, Cr solid solution induces lattice distortion of α-Al, and the Fe and Ni from 316L refine equiaxed grains. Consequently, the as-printed AlMgErZr-2.5 wt%316L alloy exhibits an ultimate tensile strength of 587 MPa with 10.5% elongation. Especially, post-aging further enhances strength to 686 MPa (retaining 5.4% elongation), attributed to L1₂ re-precipitation at both amorphous/α-Al and α-Al/α-Al interfaces. This work establishes a framework for designing crack-resistant, high-performance aluminum alloys via in-situ engineering of amorphous/crystalline heterostructures.