Influence of laser powder bed fusion scanning strategies on the magnetic and mechanical properties of NdFeB

Abstract

Laser powder bed fusion is an advanced additive manufacturing technique that can produce fine microstructures through various scanning strategies. These microstructural changes have a profound effect on the magnetic and mechanical properties of NdFeB, thus providing new opportunities for performance optimisation. In this paper, the effects of different laser interlayer transition angles of 0°, 67° and 90° as well as laser remelting on the microstructure, magnetic and mechanical properties of NdFeB are investigated. The results show that increasing the volumetric energy density increases the relative density of the magnet, but decreases the precipitation of the hard magnetic phase Nd 2 Fe 14 B and produces thermal cracks with a width of 10 µm in the build direction. Laser remelting increases the relative density by 5–10 %, and the high cooling rate of the melt pool during remelting hardly reduces the remanent magnetisation. In addition, grain orientation and microstructure combine to influence the magnetic properties of NdFeB, with Nd 2 Fe 14 B grains having the largest < 001 > orientation at a laser interlayer transition angle of 67°, whereas grains with optimal C-axis orientation and smaller grain size at an interlayer transition angle of 90° have the largest magnetic properties, with a value of 13.8 kJ/m 3 . Finally, uniaxial tensile tests were carried out on LPBF NdFeB, and the fracture morphology showed three types, with the maximum tensile strength less than 3 MPa. The presence of numerous thermal cracks and the lack of involvement of certain NdFeB grains in mechanical stretching are the primary reasons for the tensile strength falling short of its theoretical value. This study offers a theoretical foundation for enhancing magnetic performance through the optimization of LPBF process parameters. • Increasing the bulk energy density reduces the precipitation of the Nd 2 Fe 14 B phase. • Long linear laser scans have higher magnetic properties than short linear scans. • The use of two remelts with low energy density hardly reduces the remanence. • Laser interlayer transition 90° has the smallest average grain size. • Cracks formed during the forming process are the cause of low tensile strength.

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