Improving the thermal stability of sintered NdFeB magnets with nickel electroplating by high temperature treatment

Sintered NdFeB magnets with nickel electroplating are widely used in the fields of new energy vehicles, wind generators, elevators and so on. A critical issue that the NdFeB industry is faced with is the poor magnet thermal stability, i.e., a large amount of magnetic flux irreversible loss occurs when experiencing high temperature exposure. One way to address the issue is by adding heavy rare earth (RE) elements, while their scarcity, high cost, and negative effect on Br are unignorable. In this paper, by a simple heat treatment of the NdFeB substrate at 450 ℃, the thermal stability of the final coated NdFeB is significantly improved with the irreversible loss of magnetic flux decreasing from 3.49 % in the original sample to 1.85 % in the optimized sample, while maintaining excellent magnetic properties. Relations between microstructure and thermal stability are further analyzed. This study provides an easy and low-cost method of improving the thermal stability of NdFeB magnets.