Improving overlapping quality of 316L stainless steel fabricated by multi-laser powder bed fusion through optimizing non-remelting scanning strategy

Multi-laser powder bed fusion (ML-PBF) has emerged as a promising solution for achieving large-scale functional parts with high resolution based on powder bed fusion technology, particularly in high-end fields (e.g. aerospace). However, ML-PBF processes are often challenged by issues like poor surface quality, internal defects, and low mechanical properties within the multi-laser overlap region. Therefore, it is necessary to investigate a multi-laser scanning strategy to develop an effective solution for controlling overlap region quality. In this work, two non-remelting scanning strategies, sequential scanning and reverse scanning, with different scanning angles (0°, 45°, 90°) were proposed to improve the ML-PBF quality. The results show that the orthogonal sequential scanning strategy with a scanning angle of 0° resulted in a flatter surface and fewer internal defects in the overlap region. Subsequently, the influence mechanism of overlap region width (ORW) under the above-mentioned scanning strategy on surface morphology, pore defects, microstructure, and mechanical properties was systematically investigated. The sample with an ORW of 1.5 mm displayed the highest ultimate tensile strength of 625.0 MPa and elongation of 36.2 %, which is comparable to the counterparts fabricated by single-laser powder bed fusion with a negligible reduction of ~2.1 % in the tensile strength. Moreover, the fracture occurred away from the overlap region during tensile testing, which means that the suggested non-remelting scanning strategy successfully enhances the quality of the overlap region. Generally, this study provides significant insight into the quality controlling in the overlap region of ML-PBF parts and theoretical guidance for enhancing the ability to fabricate large-scale parts based on powder bed fusion technology.