Effect of SiO2 nanopowders on magnetic properties and corrosion resistance of sintered Nd–Fe–B magnets

To improve the magnetic properties and corrosion resistance of magnet, SiO2 nanopowders were added into Nd28.25Dy2.75FebalAl0.15Ga0.1Nb0.1B0.98-sintered magnets as grain boundary modifiers. It was found that the intrinsic coercivity (Hcj), remanence (Br) and corrosion resistance were all improved with addition of certain amount of SiO2 nanopowders. The optimum addition amount of SiO2 nanopowders was found to be 0.01 wt%. Thermodynamic calculation in combination of energy dispersive X-ray spectroscopy (EDX) analyses indicated that SiO2 nanopowders reacted with Nd of Nd-rich phase. As a result, the intergranular phase was modified, and the grain growth of main phase was restrained. It led to the optimization of microstructure.