Underlying role of micro-area energy input mode on formability and performance of high-strength aluminum alloy processed by micro laser powder bed fusion (μ-LPBF)

Micro laser powder bed fusion (μ-LPBF) additive manufacturing technology has significant advantages in forming extremely fine metallic structures, but controlling the laser scanning mode and attendant heat input in small areas has become much more difficult. In the present work, the regulation mechanisms of thermal flow characteristics on flaw control and performance evolution exhibited a pivotal role in fabricating high-strength Al-Mg-Sc-Zr alloys via μ-LPBF. Based on the simulation-guided laser printing path design, the effects of energy input mode on μ-LPBF formability, grain distribution and mechanical anisotropy were systematically studied in this work. Experimental results demonstrated that periodic intensive long-range variation scanning effectively enhanced melt uniformity and the dimensional accuracy of the fine lattice structure, achieving the smallest average flaw volume of 2.62 × 10⁻⁶ mm³ and near-full density (99.94 %). Due to the double exposure and intrinsic heat treatment, the long range regular remelted samples possess the least residual stress of 53.7 ± 1.8 MPa and the decreased precipitate density (1.78 ×10²⁴ mm⁻³) of the secondary Al₃(Sc, Zr) precipitates after aging treatment. The transient thermal accumulation induced unstable flow patterns that intensify pore cluster at the overlap regions, acting as three-dimensional interconnected networks of potential crack propagation pathways and it led to a remarkable deterioration of elongation. In contrast, rotational thermal flow mode enabled periodic reconstruction of thermal gradients, endowing horizontally aged specimens with superior strength-ductility synergy (UTS of 579.21 ± 3.35 MPa and elongation of 11.94 ± 2.32 %) and ignorable mechanical anisotropy induced by building direction. Fractography-coupled EBSD results of short-range dispersion mode samples reveals the combination of crack propagation along < 001 > texture orientations and the strain localization that induced by pores clusters in island boundary is responsible for the mechanical properties anisotropy. Conclusions in this work will advance the understanding of the printing mode-microstructural features and mechanical properties relationships for high strength aluminum alloy fabricated by μ-LPBF. It also provides a reference for the high-quality fabrication of the miniaturized metallic structures with fine features and satisfactory surface quality.