Coercivity enhancement of NdFeB sintered magnets by low melting point Dy32.5Fe62Cu5.5 alloy modification

• Low melting-point Dy32.5Fe62Cu5.5 alloy was introduced to NdFeB magnets.
• The doped magnet exhibits enhanced coercivity and maximum energy product.
• (Nd,Dy)2Fe14B shell was expected to form in the surface of Nd2Fe14B grains.
• The continuous grain boundary layer formed between neighboring Nd2Fe14B grains.

To improve coercivity without sacrificing other magnetic performance of NdFeB sintered magnets, a low melting point Dy32.5Fe62Cu5.5 alloy was introduced as an intergranular additive. Magnetic properties and microstructure of the magnets with different Dy32.5Fe62Cu5.5 contents were studied. At the optimum addition of 3 wt%, coercivity Hcj was enhanced from 12.7 to 15.2 kOe, the maximum magnetic energy product (BH)max was simultaneously increased from 46.6 to 47.8 MG Oe, accompanied by a slight reduction in remanence Br. Further investigation on microstructure and grain boundary composition indicated that the enhanced Hcj and (BH)max could be attributed to the refined and uniform 2:14:1 phase grains, continuous grain boundaries and a (Nd,Dy)2Fe14B hardening shell surrounding the 2:14:1 phase grains.