Effects of laser cutting and post-processing on the microstructure and properties of thin sintered Nd-Fe-B magnets

Abstract

Laser cutting, recognized for its narrow kerf, high efficiency, and adaptability to complex geometries, is increasingly employed in the machining of thin sintered Nd–Fe–B magnets. This work systematically evaluates the influence of laser cutting versus conventional multi-wire cutting combined with grinding on the microstructure, mechanical strength, and magnetic properties of magnets under black, chamfered, and pickled conditions. Laser cutting induces stepped demagnetization curves, lowers intrinsic coercivity and mechanical properties compared to conventional multi-wire cutting combined with grinding method. Results indicate that chamfering improves the three-point bending force of laser-cut samples by approximately 31.4% on average. After pickling, the specific magnetic moment of laser-cut samples is only 0.13% lower, and the irreversible flux loss is merely 0.08% higher than that of ground specimens. Microstructural analysis reveals that laser-cut surfaces contain a resolidified layer, micropores, and networked microcracks, which contribute to the degradation in mechanical and magnetic properties. Magnetic domain observations further demonstrate that laser-cut black samples exhibit blurred domain boundaries and maze domains, whereas chamfered specimens show a marked reduction in maze domains and improved domain alignment. Under identical reverse magnetic fields, domain reversal occurs more readily in black samples than in chamfered ones. In summary, through appropriate parameter selection and post-processing, such as chamfering and pickling, the mechanical and magnetic performance of laser-cut thin Nd-Fe-B magnets can closely match that of ground magnets, offering valuable guidance for process optimization in thin magnet manufacturing.