The Effects Of Nd Content And Main Phase Structure On Magnetic Properties In Nd-Fe-B/Dy-Fe-B Magnets

The actual low coercivity of Nd-Fe-B permanent magnet material seriously affects its application range,and adding heavy rare earth elements is one of the effective meth ods to improve the coercivity of magnets.In this paper,added a certain amount of Dy-Fe-B powders into Nd-Fe-B powders to prepare Nd-Fe-B/Dy-Fe-B composite magnets with dual main phase structure.By regulating the content of Nd element of Nd-Fe-B,optimized the main phase structure and element distribution,in order to obtain high remanence,high energy product and high coercivity in rare earth permanent magnets.Nd-（Fe,M）-B sintered magnets was prepared by adding Cu,Co,Zr,Ga and other elements in the Nd-Fe-B magnet.As the content of Nd decreases in Nd-（Fe,M）-B,the remanence of the magnet increases and the coercive force decreases.Reducing the Nd element content in the Nd-Fe-B magnet,the main phase of R₂Fe₁₄B is unchanged,while the volume fraction of the intergranular rare earth-rich phase（Nd-rich phase）decreases and their distribution is more uniform in the magnet,and the volume fraction of the Nd₂Fe₁₄B phase increases relatively.The decoupling effect is weakened and the coercive force is reduced.Since Nd₂Fe₁₄B phase has a high saturation magnetization,and its volume fraction increase is beneficial to improve the remanence in the sintered magnet.As the Nd content is 29 wt.%,the remanence of the Nd₁₃（Fe,M）₈₁B₆ magnet is 14.73 k Gs,the coercivity is 7.69 k Oe,and the magnetic energy product is 51.21 MGOe.Nd₁₃（Fe,M）₈₁B₆ powders and 10 wt.%Dy₁₉Fe₇₅B₆ powders were mixed to prepare a composite magnet,and the total rare earth content is 30.3wt.%,and the content of Nd element in Nd₁₃（Fe,M）₈₁B₆ is 29 wt.%.The remanence of the magnet is 14.05 k Gs,the coercivity force is 18.17 k Oe,and the magnetic energy product is 48.07 MGOe in the composite magnet.Compared with the magnetic properties in the composite magnet in which the Nd element content is 29.5wt.%,the remanence is increased by 0.06 k Gs,the coercivity is decreased by 2.65 k Oe,and the magnetic energy product is increased by 0.47MGOe.Reducing the content of Nd element can effectively reduce the volume fraction of the intergranular rare earth-rich phase in the magnet.Statistical analysis of the average element content in the composite magnet shows that as the Nd content is low,the diffusion effect of Nd and Dy elements in the magnet is weak,and that there is still a large amount of Nd₂Fe₁₄B phase.So the remanence and magnetic energy product decrease a little,and since effects of Dy₂Fe₁₄B phase and（Nd,Dy）₂Fe₁₄B phase inside the magnet,the coercive force of the magnet is significantly improved due to their high magnetocrystalline anisotropy field.In the Nd_12.2Fe_81.8B₆/Dy H_x magnet with a single main phase structure prepared by the traditional double alloy method,besides Nd₂Fe₁₄B main phase and there is（Nd,Dy）₂Fe₁₄B phase shell with high magnetocrystalline anisotropy field due to the diffusion of Dy elements.As the magnetic field reaches a certain strength,the main phase will be reversed magnetically.In the Nd₁₃（Fe,M）₈₁B₆/Dy₂₁Fe₇₃B₆ composite magnet with dual main phase structure,besides（Nd,Dy）₂Fe₁₄B shell phase formed by the diffusion between Nd and Dy elements there is the Dy₂Fe₁₄B main phase with ultro-high magnetocrystalline anisotropy field.When the magnetization reversal process starts,the Dy₂Fe₁₄B phase will inhibit the nucleation of the magnetization reversal field in the Nd₂Fe₁₄B phase,leading to the further increase of the coercivity.This dual main phase structure makes the coercive force increase significantly in the composite magnet,while the remanence and magnetic energy product decrease a little.Therefore,the overall magnetic performance of the magnet can be further improved by optimizing the phase structure and element distribution in the magnet.