Abstract: Rapid cooling and solidification during laser additive manufacturing (LAM) can produce ultra-fine microstructure with higher strength. However, the non-uniform cell/grain structure can easily result in early stress concentration and fracture during deformation, which remains a major challenge for the LAM field. Using Al-12Si as the model alloy, we employed the external static magnetic field (SMF) to modulate the laser powder bed fusion process (L-PBF), demonstrating a uniform microstructure with a refined cell structure. The mechanical properties show that the SMF can produce a combination of high tensile strength of 451.4 ± 0.5 MPa and large uniform elongation of 10.4% ± 0.79%, which are superior to those of previously-reported Al-Si alloys with post-treatment or element alloying. The mechanism analysis based on multi-scale simulation reveals the determining role of SMF in rapid solidification, and this method is applicable to the microstructure control of other metallic materials during LAM.

Key words: Laser powder bed fusion, Magnetic field, Al alloys, Grain refinement, Strengthening mechanism