| As a new type of functional material, Bonded Nd-Fe-B magnets are widely used in computers, instruments, telecommunications, automobiles, household appliances and many other fields because of their high-precision size, good form freedom, low cost and easily processed characteristics. Till now, bonded Nd-Fe-B magnetic powder (MQ powder) produced by Magnequench International INC is used widely in the world. Magnequench International INC depends on its patent and monopolizes the production of MQ powder, which limits the development of bonded Nd-Fe-B industry.HDDR magnetic powder and nanocomposite magnetic powder are two new type of bonded Nd-Fe-B magnetic powder, which can replace MQ powder potentially because of their low cost and high properties, and they are not limited by the patent. But the product technology for two type of magnetic powder is instable, and declines their magnetic properties. So it is necessary to study the composition and technology for the two type of magnetic powder.High property anisotropic Nd-Fe-B magnetic powder, Nd2Fe14B/α-Fe and Fe3B/Nd2Fe14B nanocomposite magnets were produced by modified HDDR process and rapid quenching process. The effect of preparation technology, additive elements and crystallization treatment on the magnetic properties and microstructure of magnets was studied, and magnetic hardening mechanism of magnet was analyzed. DTA and XRD were used to study phase composition and phase change process. The main conclusions are listed as follows:1. The effects of HDDR process on the properties of Nd-Fe-B alloys were investigated. The results show that:in the HD stage, anisotropic Nd-Fe-B magnetic powder with high maximum magnetic energy product is obtained when the hydrogen pressure in low temperature HD stage and high temperature HD stage is 0.09MPa and 0.02MPa-0.03MPa respectively. In the DR stage, high coercivity and excellent comprehensive properties are obtained by high vacuum treatment, and the combination of low vacuum treatment and high vacuum treatment can increase the anisotropy of alloy effectively. Study of XRD on the Nd-Fe-B alloy shows that the phase change process of Nd-Fe-B alloy in HD stage is Nd+H2'NdH2, Nd2Fei4B+H2--NdH2+a-Fe+Fe2B, and the phase change process of Nd-Fe-B alloy in DR stage is NdH2'Nd+H2,NdH2+α-Fe+Fe2B'Nd2Fe14B+H2.2. Addition of Co can increase the coercivity, anisotropic factor (DOA) and maximum magnetic energy product of Nd12.5Fe80.4-xCoxGa0.5Zr0.1B6.5 (x=0、12、15、17、20) alloys. The optimum comprehensive properties are obtained when the content of Co addition is 15at%. The HDDR treatment process:room temperaturex 0.09MPax1h'820℃x0.025MPax2.5h--820℃xhigh vacuumx0.5h. The optimum comprehensive properties show:Br=1.27T, (BH)max=245.7kJ/m3, jHc=754.3kA/m, DOA=0.62. Till now, the properties of alloy have reached domestic leading level. If the product technology can be steadied, the development of bonded Nd-Fe-B magnet will be greatly promoted.3. Addition of Ga can increase the coercivity, anisotropic factor (DOA) and maximum magnetic energy product of Nd12.5Fe68.9-yCo12GayZr0.1B6.5 (y=0、0.1、0.3、0.5、0.7) alloys. The optimum comprehensive properties are obtained when the content of Ga addition is 0.3at%. The HDDR treatment process:room temperaturex 0.09MPax1h'820℃x0.03MPax3h'820℃xhigh vacuumx0.5h. The optimum comprehensive properties show:Br=1.22T, (BH)max=218.3kJ/m3, jHc=751.2kA/m, DOA=0.52.4. Addition of Nb can increase the coercivity, but decline the remanence, maximum magnetic energy product and anisotropic factor (DOA). The optimum comprehensive properties are obtained when the content of Nb addition is 1.0at%. The HDDR treatment process:room temperaturex 0.09MPaxlh'820℃x0.03MPax3h'820℃xhigh vacuumx0.5h. The optimum comprehensive properties show:(BH)max=105.7kJ/m3, Br=1.10T, jHc=592.8kA/m, DOA=0.48.5. Nd8Fe87B5 alloy was produced by rapid quenching process, and the effect of roll speed on the magnetic properties of rapid quenching samples was studied. The results show that the magnetic properties of samples are increased with increasing roll speed. When the roll speed is 35m/s, the optimum magnetic properties are obtained. The optimum magnetic properties show:Br=0.84T, jHc=356.8kA/m, (BH)max=57.36kJ/m3. After that, the magnetic properties decline. When the roll speed is 45m/s, the rapid quenching sample of Nd8Fe87B5 alloy is amorphous, and crystallization temperature of the sample is 670℃, crystallization process shows:Am(amorphous)'Nd2Fe14B+α-Fe. The optimum magnetic properties are obtained by crystallization treatment (690℃x10min). The optimum magnetic properties show: Br=0.91T, jHc=362.7kA/m, (BH)max=73.6kJ/m3.6. Nd3.5Dy1Fe73-xCo4CuxB18.5 (x=0,0.2,0.5,0.8,1.0) alloys were produced by rapid quenching, and the effect of Cu on the magnetic properties of alloys was studied. The results show that addition of Cu can improve the coercivity and maximum magnetic energy product of alloys and the optimum content of Cu is 0.2at%. When the roll speed is 30m/s, the rapid quenching sample of Nd3.5Dy1Fe72.8Co4Cu0.2B18.5 alloy is amorphous, and crystallization temperature of the sample is 605℃, crystallization process shows: Am(amorphous)'Am’(remanent amorphous)+Nd3Fe20B2+Fe3B'Nd2Fe14B+Fe3B. The optimum magnetic properties are obtained by crystallization treatment (690℃×10min). The optimum magnetic properties show:(BH)max=91.7kJ/m3, Br=0.97T, jHc=369.6kA/m. |
PDF Full Text Request