Hot Forward-Extruded Nanocrystalline Anisotropic Nd-Fe-B Magnetic Sheets with High Magnetic Properties

Anisotropic Nd-Fe-B magnets have been fabricated by the hot forward-extrusion method and exhibit the same heterogeneous microstructure characteristics as conventional die-upsetting magnets. It has been found that the magnetic properties on both sides of the magnetic sheet are better than that of the middle zone, and that the magnetic properties of the intermediate zone in the extrusion direction are better than those of the top zone (close to the extrusion die and the latest extruded zone) and the bottom zone (the earliest extruded zone) in the extrusion direction. With the decrease of extrusion speed, the process by which Nd2Fe14B grains become flat platelets with their c-axes parallel to the stress axis by grain rotating and diffusion slip have been more fully completed, while the texture, remanence, and maximum magnetic energy product (BH)max of the forward-extruded magnetic sheet monotonically increased. With the increase of hot-pressing and hot-extrusion temperatures, the texture, remanence, and (BH)max of the hot-extruded magnetic sheet initially increased and then decreased. The magnetic sheet hot-pressed at 550°C and hot-extruded at 850°C with an extrusion speed of 0.05 mm s−1 had the best magnetic properties, its (BH)max being 40.3 MGOe, Br 13.5 kGs, and Hcj 9.8 kOe.