Abstract
In order to realize the secondary use of Nd-Fe-B magnet scraps, Nd-Fe-B recycled magnets have been widely applied. However, the poor corrosion resistance due to the rare earth oxide (RE-O) in grain boundary limits their application. In this work, 0.3 wt% of Cu powder with average grain size of 1 μm was added to improve the corrosion resistance of Nd-Fe-B recycled magnet. In comparison with the initial Nd-Fe-B recycled magnet, mass loss of accelerated corrosion test after 168 h for the Cu-modified Nd-Fe-B recycled magnet dramatically drops from 30.35 mg/cm2 to 0.0078 mg/cm2. Correlated with XRD Rietveld refinement and TEM results shows that the improved corrosion resistance is attributed to the crystal structure of RE-O change at the grain boundary phase from hcp/amorphous with high oxygen content to the Cu-rich GB phase with lower oxygen content at triple junctions after Cu modification. The formed new grain boundary phase in the Cu-modified magnet possesses low relatively Volta potentials, contributing to the enhancement of anti-corrosive properties. This work paves an effective way to obtain optimal corrosion resistance and maintain high magnetic properties simultaneously in Nd-Fe-B recycled magnet, which is beneficial to recycling of waste magnets.
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