Improvement of the coercivity and corrosion resistance of Nd–Fe–B sintered magnets by intergranular addition of Tb62.5Co37.5

•A low melting point eutectic alloy Tb62.5Co37.5 as a grain boundary additive was designed and prepared in accordance with the binary alloy phase diagram.•With the addition of 0.5 wt% Tb62.5Co37.5 powders, the remanence increased from 11.1 to 11.86 kGs owing to the optimization of microstructure of the magnet.•The intrinsic coercivity of the magnet was significantly improved due to the formation of an ideal (Nd, Pr, Tb)2Fe14B core–shell structure.•The remarkable improvement in the corrosion resistance of the magnet owing to the optimization of the composition of the grain boundary phase. To increase the coercivity and corrosion resistance of Nd–Fe–B sintered magnets in high temperature and highly corrosive environments, low melting point Tb62.5Co37.5 alloy powders were added to the starting magnets through intergranular addition. In this study, the magnetic properties, corrosion resistance, and microstructure of magnets were investigated after adding various contents of Tb62.5Co37.5 powders. The coercivity of the magnet was significantly improved from 18.20 to 27.10 kOe when a small amount of Tb62.5Co37.5 powder was added; also, the remanence first increased and then slightly decreased. The microstructure and composition of the modified magnets were studied; it was found that the significant increase in coercivity and the negligible reduction in remanence is because of the densification, improved grain alignment, uniform and continuous Nd-rich phase distribution, as well as the generation of a (Nd, Pr, Tb)2Fe14B “core–shell” structure surrounding the main phase grain. Furthermore, the corrosion resistance of the magnets was improved significantly owing to the reduction in the electrochemical potential difference between the Nd2Fe14B main phase and the Nd-rich phase.