The Study Of Preparation And Coercivity Enhancement Of RE₂Fe₁₄B Cost-effective Rare Earth Permanent Magnets

Reducing the rare earth content through fabricating Nd2Fe14B/α-Fe nanocomposite permanent magnets and fabricating La,Ce-rich abundant rare earth permanent magnets are important ways to make full use of the rare earth resources and improve the costeffectiveness of rare earth permanent magnets.However,the coercivity of Nd2Fe14B/α-Fe nanocomposite permanent magnets and abundant rare earth permanent magnets are low.Further improving coercivity is the key to promote the application of cost-effective rare earth permanent magnets.In this work,the influences of oxides and alloys dopants,preparation methods on the coercivity of rare earth permanent magnets were discussed in detail.Nd2Fe14B/α-Fe nanocomposite permanent magnets were fabricated by mechanical alloying.The influence of Dy2O3 doping on the magnetic properties of the nanocomposite permanent magnets was studied in detail.Then abundant rare earth permanent magnets were prepared by selecting the low cost mix rare earth alloy as raw materials.The magnetic properties of the permanent magnets were investigated via the Dy2O3 and Ca doping.The abundant rare earth permanent magnets were also fabricated by melt spinning and the influences of the wheel velocity,annealing temperature and the doping of Co,Zr were also analysed.The main achievements are shown as below:Nd2Fe14B/α-Fe nanocomposite permanent magnets were fabricated by mechanical alloying and post annealing process.On increasing amount of Dy2O3,the coercivity of the composite magnets grew consistently.The maximum coercivity was achieved with 7 wt.% Dy2O3 addition after annealing at 700 ℃,which was 1.7 kOe higher than the Dy2O3-free sample.By the analysis of phase compositions and magnetic performances,the improvement of coercivity can be attributed to the Dy substituted for Nd and formed(Nd,Dy)2Fe14B phases with the higher magnetocrystalline anisotropy.In terms of the above progress,RE13.6Fe78.4B8 abundant rare earth permanent magnets were prepared by using the cheap industrial mixed rare earth alloy(RE100 = La30.6Ce50.2Pr6.4Nd12.8)with La and Ce accounting for 80 at.%.Dy2O3 and Ca were co-doped to improve the utilization of Dy2O3 considering that Ca can introduce the reduction-diffusion process through reducing Dy2O3 due to a low standard electrode potential.By the co-dopants of Dy2O3 and Ca,the coercivity was significantly enhanced from 2.52 kOe to 11.43 kOe.It was determined that the rich-Dy particles in matrix were the main reason of coercivity promotion through the analysis of the microstructure.The melting spinning was also conducted to prepare RE13.6Fe78.4B8 abundant rare earth permanent magnets and the obtained coercivity reaches up to 7.15 kOe at the wheel velocity of 35 m/s,which increased 4.63 kOe than the magnets with the same composition fabricated by mechanical alloying.Then RE13.6Fe74.9Co3.5B8 and RE13.6Fe74.9Zr3.5B8 were fabricated by 3.5 at.% Co and Zr replacement for Fe,respectively.It was found that Co can obviously improve the TC and the thermal stability of the magnets,while Zr can refine the grains and have pinning effect in the magnetization process.Strong exchange coupling exist in RE13.6Fe78.4B8 abundant rare earth permanent magnets by the nanlysis of Henkel curves.