Effect of Adding Ho63.3Fe36.7 to Grain Boundaries on Structure and Properties of Regenerated NdFeB Magnets

A high-efficiency and green physical method was proposed to clean the surface of NdFeB waste magnets for recycling. NdFeB regenerated magnets were fabricated by adding low-melting point Ho63.3Fe36.7 alloy to grain boundaries. Results show that in magnets without Ho63.3Fe36.7, there are insufficient Nd-rich phases to isolate the Nd2Fe14B phase, leading to poor magnet performance. With the addition of Ho63.3Fe36.7 alloy, the grain boundary phases become clear and concatenated. Optimal magnetic energy [(BH)(max)+H-cj=1756.07] can be obtained by adding 2wt% Ho63.3Fe36.7 to the magnet. Further, the coercivity increases by 123 kA/m (approximately 9.1%), the maximum magnetic energy product decreases from 290.94 kJ/m(3) to 281.07 kJ/m(3), and remanence decreases slightly. Through analysis of the microstructure and composition, it can be seen that the (Nd, Pr, Ho)(2)Fe14B shell layers form at the grain boundary, which enhances the coercivity of the magnet. X-ray diffraction analysis suggests that the diffraction peak intensity ratio of magnet I-(006)/I-(105) increases from 0.92 to 1.32, which indicates that the alignment degree is improved and the influence on remanence is weakened. Therefore, regenerated magnets can possess improved coercivity while maintaining magnetic remanence.

Automated summary

By adding Ho63.3Fe36.7 alloy to the waste magnets, improvements in magnetic properties can be achieved in the regenerated magnets, increasing coercivity and decreasing maximum magnetic energy product. Additionally, the grain boundary phases in regenerated magnets enhance their coercivity, positively affecting the maintenance of magnetic remanence.