Coercivity enhancement via synergetic effect of dual-alloy and grain boundary diffusion strategies in Nd-Fe-B permanent magnet

A combined Nd-Rich dual-alloy and subsequent DyH2- grain boundary diffusion process (GBDP) method is proposed to improve the coercivity of Nd-Fe-B permanent magnet with reduced heavy rare metal consumption. Microstructure analysis shows Nd element was enriched in the grain boundaries and formed continuous grain boundary phases upon dual-alloy treatment, which is beneficial to decouple exchange effect between grains and provide effective channels for the subsequent diffusion of Dy during GBDP. As a result of the synergetic effect of dual-alloy and GBDP method, the coercivity was enhanced significantly by 67 %, from 1103.25 to 1842.74 kA/ m. Further Electron Probe Micro-Analysis (EPMA) and Energy Dispersive X-ray spectroscopy (EDS) character-izations revealed that the enhancement mechanism lies in the fact that Dy-rich shell is much thinner and deeper from surface to interior in the magnet treated by dual-alloy and GBDP combination. The continuous Dy-rich shell prevented the reversed magnetic domain nucleation and contributed to higher effective coercivity enhancement. The present work offers a practical modification method in Nd-Fe-B permanent magnet with the merits of lower heavy rare earth consumption, easy handling and reduced production cost.