Study On Microstructure And Magnetic Properties Of Nd-La-Y-Fe-B Permanent Magnetic Materials

High-abundance rare earth elements（Ce,La,Y）are widely used in Nd Fe B permanent magnet materials due to their high reserves and low prices.However,the intrinsic magnetic properties and curie temperature of the corresponding RE₂Fe₁₄B phase are lower than that of the Nd₂Fe₁₄B phase,it is difficult to obtain cost-effective Nd Fe B magnets.Therefore,For this reason,the Nd-La-Y-Fe-B permanent magnet material with high cost performance was obtained via melt-quick quenching method and surface coating method in this paper.Nd_27-xLa₃Y_xFe_balAl_0.1Cu_0.1B₁（x=0-3,wt.%）alloys were prepared by melting quenching method to obtain cost-effective Nd Fe B-based permanent magnets,and the magnetic properties,phase composition and microstructure were examined.When x=1.8,coercivity of 12.6 k Oe and the magnetic remanence of 7.5 k Gs were obtained,which are close to those of the original Nd₃₀Fe_balAl_0.1Cu_0.1B₁alloy ribbons without high-abundance rare earths.The temperature coefficient of coercivity（β）and the temperature coefficient of remanence（α）of the La Y-substituted alloys are higer than those of the original alloys.The research results manifest that La is mainly distributed in the grain boundary phases and plays the role of refining the main grains,optimizing the grain boundary phases and improving the wettability between the main phase and the grain boundary phase,while Y tends to enrich in the main phases and enhances effect of the short-range exchange coupling.Meanwhile,the temperature coefficient of coercivity（β）and the temperature coefficient of remanence（α）of the alloy are also improved due to the existence of Y.Pr₇₀Cu₂₀Ga₁₀（at.%）low melting point alloy was selected as the diffusion source,and commercial Nd-La-Y-Fe-B permanent magnets were annealed at high temperature by surface coating to explore the best annealing process.The study showed that the strongest magnetic properties were obtained when the magnets were annealed at 930°C/8 h,the H_cj,B_rand（BH）_maxincrease from 14.3 k Oe,11.35 k Gs,31.47 MGOe to 18.3 k Oe,11.58 k Gs,33.23 MGOe.The detection results such as XRD and EPMA indicate that the Pr from the diffusion source enters the grains and partially replaces the La in the main phases,which improves the H_Aand M_Sof the 2:14:1 phases.In addition,Ga and Cu elements enhance the clarity and continuity of the grain boundary phase,and isolate the short-range exchange coupling between the main phase grains,and thus enhance the H_cjof the magnet.Nd₇₀Cu₃₀,Nd₇₀Al₁₀Cu₂₀and Nd₆₀Dy₁₀Cu₃₀（at.%）low melting point alloy as the diffusion source were diffused in commercial Nd-La-Y-Fe-B permanent magnets at high temperature.By comparing the magnetic properties,the diffusion of Nd₆₀Dy₁₀Cu₃₀（at.%）source provides the highest increase in the coercivity of the magnet,and the H_cjis increased by about 5 k Oe.Magnetic performance improvement is attributed to the entry of Dy into the main phase to form the hard magnetic（Nd,Dy）₂Fe₁₄B phase with"core-shell structure",but the B_r,（BH）_maxand squareness are greatly weakened.The B_r,（BH）_maxand squareness were significantly improved by reducing the amount of diffusion source by 50%,and the H_cjstill increased by 4.2 k Oe compared with the original magnet.In this paper,the effect of the composite substitution of high-abundance rare earth La/Y on the magnetic properties,phase composition and microstructure of Nd Fe B alloys was investigated,and the grain boundary diffusion technology about commercial magnets containing La/Y was explored to eliminate the magnetic property defects of Nd Fe B magnets（alloys）.The reference was provided for a further study of the permanent magnets with high-abundance RE.