Improvement of the magnetic property, thermal stability and corrosion resistance of the sintered Nd-Fe-B magnets with Dy80Al20 addition

To improve the coercivity and thermal stability of the Nd-Fe-B sintered magnets simultaneously, the Dy80Al20 (at%) powders with low melting point were introduced into the Nd-Fe-B magnets. Additionally, the magnetic properties, microstructure and thermal stability of the sintered magnets with different amounts of Dy80Al20 were investigated. By adding a small amount of Dy80Al20, the coercivity was significantly increased from 12.72 to 21.75 kOe. As indicated by the microstructure analysis, a well-developed core-shell structure was formed in the magnets with the addition of Dy80Al20. The improvement of magnetic properties could be attributed to the refined and uniform matrix phase, continuous grain boundaries and a (Nd, Dy)2Fe14B hardening shell surrounding the matrix phase grains. With the addition of 0-4 wt% Dy80Al20 powder, the reversible temperature coefficients of remanence (α) and coercivity (β) of the magnets could be improved from −0.117 to −0.108%/°C and −0.74 to −0.66%/°C in the range of 20-100 °C, respectively. Additionally, the irreversible loss of magnetic flux (hirr) decreased sharply as Dy80Al20 powder was added. The results of temperature-dependent magnetic properties suggest that, the thermal stability of the magnets was effectively improved with the intergranular addition of Dy80Al20 alloy. Also, the corrosion resistance was found to be improved through small addition of Dy80Al20 powders This was partly due to the stability enhancement of the (Pr, Nd)-rich intergranular phase by Dy80Al20.