Enhancing magnetic properties and corrosion resistance of sintered Nd-Fe-B magnet with Dy and Ga additions by adjusting boron content

The effects of B content on the magnetic properties, corrosion resistance and microstructure of sintered Nd-Fe-B magnet containing Dy and Ga are studied in this work. As the B content increases from 0.88 wt.% to 0.94 wt.%, the intrinsic coercivity ( H cj ) of magnet increases at first and then decreases. The H cj exhibits a peak value of 22.19 kOe at 0.92 wt.% B, accompanied by the remanence ( B r ) of 13.43 kGs and the maximum magnetic energy product ( BH ) max of 43.83 MGOe. When the B content is 0.92 wt.%, the grain boundary phase (GBP) between the main phase grains simultaneously attains the widest width and the lowest Fe content, which effectively improves the demagnetization exchange coupling between the adjacent grains. Meanwhile, the RE 6 Fe 13 Ga and Ia 3 ( — ) -RE 2 O 3 phases in this magnet exhibit a small lattice misfit with adjacent main phase, which helps to reduce the nucleation of reverse domains at the GBs. The corrosion resistance of magnet can be enhanced by increasing the B content, as evidenced by the elevation in open circuit potential, the decrease in corrosion current density, and the increase in charge transfer resistance in 3.5 wt.% NaCl solution. The magnet with 0.94 wt.% B exhibits optimal corrosion resistance. By optimizing the B content in sintered Nd-Fe-B magnet with 1.8 wt.% Dy and 0.5 wt.% Ga, an intrinsic coercivity comparable to that of magnets containing 3-5 wt.% Dy and 0.91-0.98 wt.% B can be achieved, while the corrosion resistance is also enhanced to a level comparable to that of magnets containing 6-7 wt.% Dy and 1 wt.% B. • Adjusting B content can enhance the H cj and thermal stability of Nd-Fe-B magnets. • The corrosion resistance of Nd-Fe-B magnets increases as B content rises. • In B-0.92 magnet, RE 6 Fe 13 Ga and RE 2 O 3 show small misfit to adjacent 2:14:1 grains. • The continuity of GBP is good for the magnets with B contents of 0.88-0.92 wt.%. • The magnet with 0.92 wt.% B has the widest grain boundary with the lowest Fe content.