The effects of initial density on the magnetic properties of NdFeB magnets prepared by single-stage hot deformation were investigated in this work. The results show that the values of maximum energy product(BH)m and coercivity Hcjdecrease with the increase of initial density. Under optimum condition, an anisotropic magnet with a maximum energy product of 264 kJám-3was produced using the initial density of 4.4 gácm-3. The influence of initial density on the magnetic properties was discussed on the basis of microstructure and strain energy. It is concluded that the thicker platelet grains are obtained along the Nd2Fe14 B base plane with the initial density increasing.It is mainly because that grain rotation is restricted by high strain energy, which results from high initial density.
Radially oriented Nd–Fe–B ring magnets were prepared by backward extrusion of MQ-C powder. The punch chamfer radius has a great impact on the microstructure and magnetic properties of the ring magnet. With the chamfer radius changing from 2, 5 to 8 mm, the cracks in the inner wall decrease obviously while the crystallographic alignment drops. Furthermore, the mechanism of caxis growth was suggested to be a combination of shear deformation in the corner and solution-precipitation under the stress parallel to radial direction. The alignment drops on the top of ring because the grains grow freely and some textured grains grow through nucleation and recrystallization. In the present work, the optimal punch chamfer radius is found to be 2 mm, and in this case, the remanence,coercivity, and maximum energy product of the ring magnet achieve 1.4 T, 670 kJám, and 342 kJám,respectively.
