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Grain boundary diffusion of heavy rare earth-based alloys can effectively enhance the coercivity of Nd-Fe-B magnets. Although the light rare earth elements can further improve the diffusion efficiency of Dy and Tb, they generally lead to reduced anti-corrosion properties of the magnets. Here, we successfully enhanced the coercivity and corrosion resistance of Nd-Fe-B magnets by GBD of Ni alloyed Pr-Tb-Cu diffusion source. The ternary Pr 35 Tb 35 Cu 30 alloy diffusion increased the coercivity of Nd-Fe-B magnet from 1330 to 1923 kA/m, but the coercivity was enhanced to 1990 kA/m by Pr 35 Tb 35 Ni 15 Cu 15 alloy diffusion. The formation of high-anisotropy (Nd,Tb) 2 Fe 14 B phase is the main reason for the coercivity improvement. Partially substitution of Cu by Ni can reduce the melting point of Pr 35 Tb 35 Cu 30 alloy, which is effective in promoting the infiltration of Tb. Cu is also a necessary element for improving the diffusion process, and the diffusion of Pr 35 Tb 35 Ni 30 alloy only increased the coercivity to 1747 kA/m. More interestingly, the diffusion of Pr 35 Tb 35 Ni 15 Cu 15 also enhanced the chemical stability of the magnet in NaCl solution. Scanning Kelvin probe force microscopy characterized that the modified GB phase in Pr 35 Tb 35 Ni 15 Cu 15 treated magnet exhibits a higher Volta potential than the 2:14:1 main phase, which is the main reason for the improved corrosion resistance. The present results suggest that the non-rare earth elements in the alloy diffusion sources play important roles in enhancing both coercivity and corrosion resistance of Nd-Fe-B magnets. • Both coercivity and corrosion resistance of Nd-Fe-B magnet are distinctly enhanced. • Ni alloying lowers melting point of Pr-Tb-Cu and deepens the infiltration of Tb. • Ni alloying results in higher potential of grain boundary than that of 2:14:1 phase. • Scanning Kelvin probe force microscopy was used to measure local potential. [ABSTRACT FROM AUTHOR]