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 either by melt spinning or strip casting. The powders produced by these two methods show different particle shapes and sizes which may be suitable for different applications, e.g., manufacturing bonded, sintered, or hot-deformed magnets. While melt-spun powder is a good initial material for bonded and hot-deformed magnets, strip-cast powder is normally used for sintered magnets. In this study, NdFeB powders manufactured by melt spinning and strip casting were hot pressed (without particle alignment) under the same conditions. Although the processing parameters are exactly the same (pressed in the same mold), the magnetic properties of the magnets made from the two powders are significantly different. The magnet made from the strip-cast powder (after ball milling) shows reasonably good magnetic properties, with a coercivity (HcJ) of 1270 kA/m and a remanence (Br) of 0.7 T, while that made from the melt-spun powder exhibits much lower properties: HcJ = 477 kA/m, Br = 0.5 T. The magnetic properties of the initial powders and the microstructure of the pressed magnets are characterized. 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.