NdFeB Magnets Manufactured by Hot Pressing Using Strip-Cast and Melt-Spun Powders

The initial powder used for the manufacturing of NdFeB permanent magnets is usually prepared through rapid cooling, either by melt spinning or strip casting. The powders produced by these two methods are suitable for different applications: while melt-spun powder is a good initial material for bonded and hot-deformed magnets, strip-cast powder is normally used for sintered magnets. To investigate the suitability of using strip-cast powder to manufacture hot-deformed magnets, NdFeB powder prepared by strip casting was hot pressed (without particle alignment) and compared with melt-spun powder prepared under the same conditions (700 °C, 45 MPa, 90 min). Although the processing parameters are the same (pressed in the same mold), the magnetic properties of the magnets made from the two powders are significantly different. Surprisingly, the magnet made from the strip-cast powder (after ball milling) shows comparable magnetic properties to those of isotropic magnets, with coercivity (H_cJ) of 1270 kA/m and remanence (B_r) of 0.7 T, while that made from the melt-spun powder exhibits much lower properties: H_cJ = 480 kA/m, B_r = 0.5 T, although the melt-spun powder initially shows much better magnetic properties than the strip-cast powder. Possible reasons for such a difference in magnetic properties are discussed. It was shown that the particle size of the initial powder plays an important role in determining the final magnetic properties of the hot-pressed magnets.