Effects of Cu nanopowders addition on magnetic properties and corrosion resistance of sintered Nd–Fe–B magnets

Sintered permanent magnets have been prepared by blending Nd–Fe–B jet-milled powders with Cu nanopowders (0, 0.05, 0.1 and 0.2 wt%) before pressing in a perpendicular magnetic field. Permanent magnetic properties, Curie temperature (Tc), microstructures and corrosion resistance of the sintered magnets were investigated. Microstructural characterization revealed that the grain size of Nd2Fe14B phase was refined and more homogeneous, and the grain boundaries became clear and smooth by the addition of Cu nanopowders, resulting in the improvement of coercivity Hcj. Moreover, the corrosion resistance of Nd–Fe–B magnets was also improved. However, Tc remained nearly unchanged with Cu addition, which was consistent with the elemental analysis results. Cu was not detected in the matrix phase Nd2Fe14B, but concentrated in the intergranular region.