Influence of Dysprosium Distribution on Properties of Sintered and Aged Dy-doped NdFeB Permanent Magnets

Sintered and aged Dy-doped NdFeB magnets were investigated. The magnetic properties, the microstructures and the compositions were characterized by hysteresis loop instrument, thermal field emission scanning electron microscopy (TFESEM) and energy disperse spectroscopy (EDS), respectively. The results indicate that Dy element is mainly distributed in the Nd-rich phase, Nd-Dy oxides and Dy-rich particles located at the grain boundaries of the sintered magnets, in addition to the main crystal phase Nd2Fe14B. The optimized aging process is beneficial to promote a reasonable diffusion and distribution of Dy element. The Dy contents of Nd-riched phases, Nd-Dy oxide, and Dy-riched particle decrease successively in the sintered, the high temperature aged and the optimally two-stage aged Dy-doped NdFeB permanent magnets. The measurements demonstrate that the enhancement of the coercivity of the aged Dy-doped NdFeB Magnet is caused mainly by the Dy element reasonable distribution.