Thermal Stability And Comprehensive Utilization Of Rare Earth Resources In Sintered NdFeB Magnets

Sintered Nd Fe B,as the third generation of rare earth permanent magnet material,is widely used in new energy vehicles,intelligent manufacturing,medical and other high-tech industries due to its excellent magnetic properties.However,with the continuous increase of demand and output in different industries,the price of main raw materials has repeatedly set new highs,and the magnets have higher and higher requirements for coercivity and thermal stability.At present,in industry,dysprosium or terbium are often directly added during smelting to improve the coercivity of magnets and prepare Nd Fe B magnets with high comprehensive performance.However,the utilization rate of heavy rare earth is low,the production cost is high,and the remanence and magnetic energy product decrease greatly.On the one hand,through the design elements in it to join the lower prices,higher abundance of Gd elements to create excellent low price of sintered Nd-Fe-B magnet.On the other hand,by adjusting the structure of the matrix material of magnetron sputtering and improving the diffusion efficiency,a new idea is provided for reasonable and comprehensive utilization of rare earth elements.The main research contents are as follows:（1）Through adjusting Gd element content in the（Pr,Nd）_31-xGd_xFe_balAl_0.4Cu_0.2Ga_0.2Zr_0.2Co₁B_0.9 magnets,and analyses the influence of Gd contented magnet magnetic energy and the influence of temperature stability.The magnets were characterized by SEM and XRD methods to understand the microstructure by adding of Gd.The density of the magnet increases with the increase of Gd element.The maximum coercivity is 14.77 k Oe when Gd replaces 1%Pr Nd.Remanent magnetism and maximum magnetic energy product decrease gradually.With the increase of Gd content,the value of remanence temperature coefficient and coercivity temperature coefficient of the magnet decreased to-0.1080%/K and-0.6560%/K,the irreversible flux loss decreased from 27.1%to 18.8%,and the Curie temperature increased by12.64℃compared with the original magnet.The Gd-rich phase appears in the magnet with 5%Gd content,which plays a wetting role.Compared with the Nd-rich phase,the Gd-rich phase is grayer,and it replaces part of Pr Nd in the main phase to form（Pr,Nd,Gd）₂Fe₁₄B main phase structure,which improves the density and thermal stability of the magnet.（2）Through adjusting（Pr,Nd）₃₁Ga_0.2Co₁Zr_0.2Al_xCu_yB_0.98Fe_65.82-x-y of Cu/Al element in proportion.Analyses the magnetic and thermal stability of Cu/Al element not magnet and magnetron sputtering diffusion abilities by 4/7/10/13μm Tb after magnets.The effect of Cu/Al addition on its microstructure was studied by SEM and EDS characterization methods.A)The coercivity of Al element on sintered magnets is 14.82 k Oe in the magnet with 0.6%Al content.The coercivity increases by 2.48 k Oe without diffusion,and reaches 22.19 k Oe after diffusion of 13μm,79.82%higher than that of the magnet without diffusion and without adding Al element.The remanence decreases only by0.68 T,and the magnetic properties are greatly improved under the influence of Al element.The coercivity of Cu element on sintered magnets is up to 14.58 k Oe in the magnet with 0.4%Cu content.The coercivity increases by 2.24 k Oe without diffusion,and reaches 22.51 k Oe after diffusion of 13μm.Compared with the magnet without diffusion and without Cu element,the coercivity increases by 82.41%,while the remanence decreases by 0.36 T only.After diffusion,the magnetic properties are greatly improved under the influence of Cu element.B)The coercivity temperature coefficient of 7μm Tb metal coated on the surface of Al magnet reaches the maximum value-0.5601%/K at 0.6%Al content,and the irreversible flux loss（HIRR）decreases from 28.89%to 23.62%after Adding Al.The maximum coercivity temperature coefficient of Cu magnet coated with 7μm Tb metal reaches 0.5632%/K at 0.3%Cu content,and the irreversible flux loss（HIRR）at 180℃decreases from 28.89%to 24.53%after Cu/Al addition.The temperature stability of the magnet is significantly improved after Cu/Al addition.C)SEM characterization of the diffusion of 7μm Tb metal on the surface of 0.6%Al and 0.4%Cu magnets showed that the Tb-coated metal diffused from the grain boundary to the inner part of the magnets,forming the core shell structure of Tb₂Fe₁₄B.Al and Cu elements increased the proportion of neodymium-rich phase,and the diffusion effect of Tb-coated magnets was significantly enhanced.