Promoting the densification and grain refinement with assistance of static magnetic field in laser powder bed fusion

Abstract

Owing to its high accuracy and good design flexibility, the application of laser powder bed fusion (LPBF) to metallic parts has been rapidly increasing. However, the parts fabricated using LPBF exhibit high porosity and rough texture, which severely hinders the development of this technology. In this study, typical Al-based (AlSi10Mg) and Ni-based (Inconel 718) alloys were fabricated under a wide range of parameter spaces using static magnetic field (SMF) of up to 0.2 T. The experimental results showed that the fabricated parts had a higher density with SMF than the samples fabricated without SMF. A comparison of the samples fabricated with and without SMF revealed that the SMF refined the grain size and improved the mechanical properties. Furthermore, physics-based models, including the Seebeck effect, heat transfer, and fluid flow, in melt pools dynamics were used to simulate the thermos-electric-magnetic (TEM) forces and flow patterns during LPBF. The results of the simulation suggest that at the melt pool scale, the depression zone depth increases with increasing SMF intensity, and the correspondingly increased laser absorptivity is the main reason for the decrease in the lack-of-fusion defects. In addition to the flow pattern change at the melt pool scale, the TEM force acting on the cellular dendrite also plays an important role in grain refinement, reaching 105 N/m3 under a SMF of 0.1 T. Furthermore, the results of the tensile tests showed an increase in the ultimate tensile strength and elongation of the printed samples under the applied SMF. The present study can guide the porosity control and the widening of the processing window in LPBF.