Basic Research On Service Magnetic Properties Of Rare Earth Permanent Magnet Without Dy And Tb

In the industrialization context of the unbalanced development of the supply and demand side of the sintered Nd-Fe-B permanent magnet industry chain,On the one hand,the sintered Ce magnets for low and mid-end industrial motors usually still contain more expensive Pr Nd;on the other hand,the high remanence and high coercivity magnets for high-end industrial motors still cannot meet the service characteristics even with the addition of heavy rare earth Dy and Tb because the magnetic energy product of basic industrial Nd-Fe-B magnets is not high enough.Therefore,based on the theory of two-phase Ce magnets and the results of high energy product permanent magnets,this dissertation explores industrialization technologies of coercivity thermal-stable Ce magnets and high energy product Nd-Fe-B permanent magnets,and it is important to carry out basic research on the service magnetic properties of dysprosium-free terbium rare-earth permanent magnets.The main research findings obtained are as follows:（1）In response to the problem that sintered Ce magnets for low and mid-end industrial motors usually also still contain more expensive Pr Nd,repeated studies have found that a new sandwich-like grain boundary phase with crystalline RE ₆（Fe,TM）₁₁Al₃phase as the center and amorphous rare earth-rich phase symmetrically distributed on both sides of the main phase is found in Pr-Nd-Al Ce magnets.Preliminary analysis of the theoretical model shows that the"sandwich"grain boundary phase structure is characterized by self-compensating coercivity thermal stability.The nominal composition is[（Pr0.25Nd0.75）0.75Ce0.24]32.3Febal Al1.2Cu0.2Zr0.2 B0.97（wt.%）.The magnetic properties are B_r=12.0 k Gs,H_cj=14.93 k Oe,（BH）_max=34.65 MGOe.Compared to the commercial Nd-Fe-B magnets with the same performance,the thermal stability is better while saving 24%of the high-value Pr Nd metal.The industrialization of thermal-resistant stable Pr-Nd-Al Ce magnets was realized.（2）The formation mechanismof the"sandwich-like"grain boundary phase were investigated by combining the phase diagram and grain boundary regulation.The adition of Pr-Nd-Al changed the composition of the rare earth-rich phase of the magnet.During the sintering and aging process,the new Nd-rich phase had good amorphous formation ability,and the RE₆（Fe,TM）₁₁Al₃ phase preferentially nucleated and grew,and the"sandwich"grain boundary phase is formed by the interfacial tension between the Nd-rich liquid phase,the main phase and the RE₆（Fe,TM）₁₁Al₃ phase.The thickness of this grain boundary phase is 15 nm,which exceeds the exchange coupling length between the main phases,leading to enhanced main phase demagnetization coupling and improved coercivity and its thermal stability.（3）High-performance sintered Nd-Fe-B permanent magnets with a maximum energy product（BH）_max exceeding 53 MGOe and its industrialized preparation method were successfully obtained through optimizing the microstructure of the stripe casting and the key process of powder particle modification.The nominal composition of the magnet is Pr₈Nd_21.7Fe_bal.Co_0.3Al_0.03Ga_0.1Cu_0.1Zr_0.15B_0.94（wt.%）.The density of magnet is 7.56 g/cm³.The average grain size is about 6μm.The magnetic properties of the magnet are B_r=14.93 k Gs;H_cj=13.36 k Oe;（BH）_max=53.71 MGOe;H_k/H_cj=0.991.Shortening the gap of foreign magnets with high magnetic energy product.（4）The matching study of melt superheat treatment and casting temperature shows that the temperature supercooling and composition supercooling jointly affect the nucleation and growth behavior of columnar crystals in the stripe casting.Controlling the melt superheat treatment system is helpful to the uniformity of microstructure under the appropriate casting temperature.The（Ce,Nd）-Fe-B and Nd-Fe-B alloy strip casting with good columnar crystal structure and matching process were successfully obtained,which laid a foundation for the preparation of high-performance permanent magnets.For（Ce,Nd）-Fe-B alloy strip casting,the casting temperature is 1380°C,and the melt superheat is 90°C.For Nd-Fe-B alloy castings,the casting temperature is 1420°C,and the melt superheat is in the range of 60°C to 80°C.