Microstructure and Magnetic Properties of Sintered NdFeB Magnets Optimized by Electrophoretic Deposition of Al and Its Grain Boundary Diffusion

An Al film was deposited on the surface of sintered NdFeB magnets by electrophoretic deposition (EPD). It is found that different EPD voltages and times have a great influence on the deposition of Al films. We also investigated the effects of different grain boundary diffusion processes on the microstructure and magnetic properties of the magnet. The results show that the best EPD process is 90 V/30 s. At this time, the combination of the film and the magnet is well, and the thickness is even and moderate. When the grain boundary diffusion process is 500 degrees CR h, the magnet obtains the best comprehensive magnetic properties, and its coercivity, remanence and maximum magnetic energy product are 953 kA/m, 1.41 T and 342 kJ/m(3), respectively, which increases by 30.2%. 0.7% and 11.4%, respectively. Through microstructure and composition analysis, it is found that after the grain boundary diffusion, a flatter and smoother rare earth-rich phase thin layer forms between the crystals, which helps to reduce the demagnetizing field and enhance the magnetic isolation effect, and finally leads to the improvement of coercive.