Fabrication Of Low Heavy Rare-earth Sintered Nd Fe B Magnets By Dy-Fe Based Alloys Intergranular Addition

High coercivity Hc and excellent thermal stability are required more strictly since the sintered NdFe B magnets have been widely applied in high-end fields such as hybrid electric vehicles,artificial Intelligence.At present,high performance commercialized sintered Nd-Fe-B magnets have to rely on heavy rare earth elements such as dysprosi?m?Dy?and Terbium?Tb?to enhance coercivity to improve the thermal stability by using single alloy meltingmethod in industrial production.The drawbacks of this method are the deterioration of remanence Br and maximum energy product?BH?max as well as high material cost.In this study,the sintered magnets are fabricated by the intergranular addition of Dy₈₀Fe₁₃Ga₇,Pr₁₆Dy₆₄Fe₂₀,Dy₈₀Fe₂₀+Zn and Dy₈₀Fe₁₂Co₈ ternary alloy to improve their coercivity,thermal stability and corrosion resistance,which is also more effective andeconomical.The low heavy rare earth sintered Nd FeB magnets are further optimized by the heat treatment process and microstructure regulation.The results show the best comprehensive performance magnets are obtained by adding3wt.%Dy₈₀Fe₁₂Co₈ alloy.The coercivity is improved greats by about 37%while the remanent magnetization is reduced only by 4.5%.The temperature coefficients of remanence and coercivity are improved from-0.117%/?,-0.571%/?to-0.105%/?,-0.567%/?respectively in the temperature range of 20¹50°C.The irreversible flux loss of the magnet is obviously reduced after addition and the thermal stability of magnets are better off.The coercivity increases significantly by adding Dy₈₀Fe₁₃Ga₇ alloy but the remanence decreases obviously.However,the remanence decreases slightly and the coercivity is not enhanced much by adding Pr₁₆Dy₆₄Fe₂₀ and Dy₈₀Fe₂₀+Zn alloys.The optimal sintering process is 1060^oC×2 h+890 ^oC×1 h+500 ^oC×2 h.Though the annealing temperature has small impact on the remanence and maximum energy product,it greatly improves the coercivity of the magnets.RE-rich phases are formed around grains and the grain boundary wettability increases.The Dy diffuses from the grain boundary around the main phase during sintering,and forms?PrNd,Dy?₂Fe₁₄B phase.Thesse results in enhancing the magnetic anisotropy field Ha and coercivity effectively.Pr element can increase the remanence and maximum energy product of the magnet because the volume faction of main phase 2:14:1 increases.Ga atoms enter into the main phase and occupy Fe sites,leading to the reduction of remanence.Zn element has low melting point with evaporation during the sintering process,and the microstructural defects of the magnets increase.There are different potentials between Nd₂Fe₁₄B phase and RE-rich phase when the magnets are exposed in corrosive environment.RE-rich phase has low corrosion potential so that it will be corroded first.The RE₂O₃ will be formed by combining with oxygen.The binding force becomes worse,eventually resulting in the falling off of grains.The corrosion resistance of the magnets will be better off by adding Dy₈₀Fe₁₂Co₈ alloy??1.5 wt.%?.To conclude,the low heavy rare-earth sintered NdFe B magnets are fabricated by the intergranular addition of different Dy-Fe series ternary alloys,and the coercivity mechanism and corrosion principle are investigated systematically,which may shed light on the further research and give guidance on development of industrial production.