Effects Of Low Heavy Rare Earth Alloy On Microstructure And Magnetic Properties Of Hot-deformed Nd-Fe-B Magnets

Nd-Fe-B rare earth permanent magnet materials are widely used in electronic information,energy conservation,environmental protection,rail transit,aerospace and other fields due to their excellent magnetic properties.Nd-Fe-B rare earth permanent magnet materials are mainly divided into sintered Nd-Fe-B,bonded Nd-Fe-B and hot-deformed Nd-Fe-B according to their preparation methods.Compared to sintered Nd-Fe-B,the forming process of hot-deformed Nd-Fe-B magnets has the advantages of short preparation cycle,no need for external magnetic field orientation.Its structure is nanocrystalline,which is benefit to the improvement of the coercivity and thermal stability.In this paper,the original nanocrystalline anisotropic hot-deformed magnets with excellent properties were prepared by traditional hot-pressing sintering techniques.The effects of grain boundary addition of Pr₅₀Dy₂₀Cu₁₅Ga₁₅ alloy and grain boundary diffusion of Nd₅₀Dy₂₀Cu₃₀0 alloy on the coercivity and microstructure evolution of hot-deformed magnets were studied respectively.First of all,through the continuous exploration of the preparation process of hot-pressed and hot-deformed magnets,the anisotropic nanocrystalline hot-deformed magnets with excellent comprehensive properties were finally prepared under the hot-pressed condition of650?/250 MPa/2 min and the hot-deformed condition of 820?/75 MPa/5 min/72%.The remanence?J_r?,coercivity(H_cj)and magnetic energy product?BH?_max of the magnets are:J_r=1.34 T,H_cj=1242 kA/m and?BH?_max=335 kJ/m³,respectively.Due to the relatively low temperature,there are still many holes in the hot-pressed magnet,and the grains are randomly oriented equiaxed.However,due to the high preparation temperature,the hot-deformed Nd-Fe-B magnet has fewer internal holes,and its grains are c-axis oriented plate-like crystals.There is a non-oriented coarse crystal region in the contact area between the magnetic powder and the magnetic powder inside the hot-deformed magnet.When the hot-pressed magnet is heated without pressure,the grain size of the main phase of the magnet increase,but there is no orientation.Secondly,Pr₅₀Dy₂₀Cu₁₅Ga₁₅?at.%?low heavy rare earth alloy was introduced by intergranular addition technique in order to further improve the H_cj and thermal stability of hot-deformed Nd-Fe-B magnets.The effects of different Pr₅₀Dy₂₀Cu₁₅Ga₁₅5 alloy additions on the magnetic properties,thermal stability,microstructure evolution and recoil loops of hot-deformed Nd-Fe-B were studied.The results show that when the addition amount of Pr₅₀Dy₂₀Cu₁₅Ga₁₅5 alloy is 3 wt.%,The H_cj of the hot-deformed Nd-Fe-B magnets increases significantly,from 1242 kA/m to 1595 kA/m,and the remanence decreases from 1.34 T to1.22 T.At high temperatures,the thermal stability of the doped magnets was significantly improved.The strong magnetic isolation of Nd₂Fe₁₄B grains by rare earth-rich?RE-rich?phases and the formation of local high-anisotropy?Nd,Pr,Dy?₂Fe₁₄B hard magnetic phases are the main reasons for the enhancement of H_cj.The decrease of remanence is due to the poor orientation of the grains and the existence of non-oriented coarse grain regions in the contact gap of powder flakes.Further study shows that the uneven aggregation of the RE-rich phases will lead to the inhomogeneous distribution of the local magnetic anisotropy and eventually increase the opening of the recoil loops.Finally,the influence of grain boundary diffusion Nd₅₀Dy₂₀Cu₃₀ on the magnetic properties and microstructure evolution of hot-deformed Nd-Fe-B magnets were studied.By diffusion at 650?/3 h,the coercivity of the magnet is greatly improved,from 1224 kA/m to1509 kA/m.The thermal stability of the magnet has also been greatly improved.The remanence temperature coefficient and coercivity temperature coefficient have increased from-0.116%/K and-0.553%/K to-0.108%/K and-0.487%/K,respectively.Compared with the original magnet,the grain size of the diffusion sample increased,the rare earth-rich phase increased significantly,and the grain orientation decreased.The reason for the growth of the magnet grains is that the nanocrystals are very sensitive to temperature,and the reason for the decrease in the orientation of the grains may be that the introduced non-magnetic phase will aggregate at the grain boundaries,causing the magnet to expand.In this paper,the effect of low heavy rare earth alloy on the microstructure and magnetic properties of hot-deformed Nd-Fe-B magnets was systematically studied.This achievement has important academic value and practical significance for the preparation of hot-deformed Nd-Fe-B magnets with excellent comprehensive properties.