Grain Boundary Diffusion of Non-Rare Earth Al for Sintered Nd-Fe-B

Using Al powder as diffusion source, the influence of grain boundary diffusion processes on the microstructure and magnetic properties of Nd-Fe-B magnets was investigated. It is found that the optimum magnetic properties including the coercivity of 1131 kA/m and the maximum energy product of 249 kJ/m(3) can be achieved, which are increased by 16% and 9.6%, respectively compared with those of the as-prepared magnet. Meanwhile, the temperature stability is also improved. Microstructural investigation reveals that after grain boundary diffusion, Al is mainly distributed in the intergranular RE-rich phase, and the morphology of RE-rich phase changes from large block to thin layer. Smoother and straighter interface can be obtained, which can restrain the nucleation of anti-magnetization domain, reducing the demagnetization field. In addition, the Al in the intergranular phase is beneficial in elevating the corrosion potential, and the decreased corrosion current density should be attributed to the changes of RE-rich phase distribution.