The effect of powder shape on the magnetic anisotropy in NdFeB bonded magnets

Abstract

The advent of NdFeB bonded magnets with freedom of shape design is effective in achieving motor size and weight reductions. In this paper, the NdFeB bonded magnets were produced through calendaring molding, and the effect of powder shape on degree of alignment (DOA) of NdFeB bonded magnets was investigated. The magnetic measurement results demonstrate that platelet-shaped anisotropic Master Quality Authenticated (MQA) powders exhibit a significantly higher DOA compared to sphere-shaped anisotropic HDDR powders. Microstructural analysis reveals the presence of an oriented structure induced by mechanical stress in MQA bonded magnets, resulting in magnetic anisotropy. This observation is consistent with the difference in X-ray diffraction (XRD) patterns between the cross-section and surface of MQA bonded magnets. Conversely, spherical HDDR particles display minimal orientation and maintain a random distribution, resulting in magnetic isotropy. The XRD pattern of the cross-section of HDDR bonded magnets closely resembles that of its surface. In summary, our findings highlight the superior potential of platelet-shaped anisotropic MQA powders for achieving enhancing magnetic properties during the calendaring molding process, in contrast to sphere-shaped anisotropic HDDR powders. This study provides valuable insights into the determinants of mechanical particle orientation during the fabrication of anisotropic NdFeB bonded magnets, with implications for the development of high-performance bonded magnets.