Improvement of corrosion resistance and magnetic properties of Nd-Fe-B sintered magnets by Al₈₅Cu₁₅ intergranular addition

To improve the corrosion resistance and magnetic properties, Al ₈₅Cu₁₅ (at.%) compound powders were added to (Pr, Nd) _14.8Fe_78.7B_6.5 sintered magnets as grain boundary modifiers. The corrosion resistance was found to be remarkably improved by small additions of Al₈₅Cu₁₅ powders. When 1.2 wt% Al₈₅Cu₁₅ was added, the corrosion rate of magnets in humid environments was reduced by two orders of magnitude. This is partly due to the stability enhancement of the (Pr, Nd)-rich intergranular phase by Cu and Al. In addition, the occurrence of the Cu-rich phase ((Pr, Nd)₂₂Fe ₅₆Cu₁₀Al₂O₁₀), whose open-circuit potential is higher than the (Pr, Nd)-rich intergranular phase, may be another reason for the improvement of the corrosion resistance. Furthermore, the magnetic properties of (Pr, Nd)_14.8Fe_78.7B_6.5 were also improved by adding 0.3-1.2 wt% Al₈₅Cu₁₅. Optimum addition amount was 0.6 wt%. The improvement of the magnetic properties may be related to the microstructural modification and the increase of magnet density.