Effect of low heavy rare earth alloy Pr-(Dy, Y)-Al on magnetic properties and microstructure of sintered Nd-Fe-B via grain boundary diffusion

In order to reduce the cost of diffusion sources, the effects of three low-cost diffusion sources, Pr₇₀Dy₁₀Al₂₀, Pr₇₀Y₁₀Al₂₀ and Pr₆₀Dy₁₀Y₁₀Al₂₀ on the magnetic properties and microstructure of sintered Nd-Fe-B magnets were investigated using grain boundary diffusion technology. After diffusion, the coercivity of the three magnets increased from 858 kA/m to 1 746 kA/m, 1 118 kA/m and 1 572 kA/m, respectively. The Pr₇₀Dy₁₀Al₂₀ magnet exhibited the largest coercivity enhancement, reaching 203% of the original magnet. This was primarily attributed to the formation of a Dy-rich shell and a continuous rare-earth-rich grain boundary phase. In the Pr₇₀Y₁₀Al₂₀ diffused magnet, Y-rich shells with darker atomic number contrast were formed, and the diffusion depth of Y was similar to that of Dy in the Pr₇₀Dy₁₀Al₂₀ diffused magnet. Although the coercivity increase in the Pr₆₀Dy₁₀Y₁₀Al₂₀ diffused magnet was lower than that in the Pr₇₀Dy₁₀Al₂₀ diffused magnet, it still showed a significant improvement compared to the Pr₇₀Y₁₀Al₂₀ diffused magnet. Microstructural analysis revealed that in the Pr₆₀Dy₁₀Y₁₀Al₂₀ diffused magnet, Pr, Dy, and Y tended to enter the main phase, forming thicker Pr-Y-Dy-rich shells, which reduced the anisotropy of the shells and limited the improvement of coercivity.