稀土永磁材料退磁曲线及不可逆退磁对应关系研究

稀土永磁电机采用烧结钕铁硼作为励磁源,在使用过程中磁体受到高温及反向磁场的共同作用。常规情况下为了研究磁体的抗退磁性能,需模拟电机的运作工况进行分析测试。本文通过理论计算,得出磁通不可逆损失可以通过退磁曲线上高温T下测试的剩磁以及在高温T和反向磁场退磁后测试的剩磁进行计算得到。通过实验认证,该公式的可靠性,为后续研究磁体的抗退磁性能提供参照。     

高综合性能烧结钕铁硼磁体关键制备技术研究

通过优化合金成分设计和改进速凝片铸技术、烧结技术,在工业生产线上成功实现了40EH高综合性能烧结钕铁硼磁体的批量生产。SEM观察结果表明,磁体显微组织致密、精细而均匀;其平均晶粒尺寸约为5～6μm,不存在尺寸明显偏大的晶粒。在常温下,40EH烧结钕铁硼磁体的典型磁性能为Br=1.288 T,Hcb=996.8 kA.m-1,Hcj=2490 kA.m-1,Hk=2018 kA.m-1,(BH)max=322.0 kJ·m-3;其Hcj/79.6kA.m-1+(BH)max/7.96 kJ·m-3=71.7。在473 K高温下,40EH烧结钕铁硼磁体的典型磁性能为Br=1.056 T,Hcb=585.8 kA.m-1,Hcj=641.8 kA.m-1,Hk=520.2 kA.m-1,(BH)max=200.9 kJ·m-3;其J-H退磁曲线方形度较好,B-H退磁曲线仍然表现出比较明显的线性特点。在295～473 K温度区间,其剩磁与内禀矫顽力的温度系数分别为-0.101和-0.417(%.K-1)。当L/D=0.7时,在493 K保持2 h磁体开路磁通不可逆损失为3.8%左右。批量生产的40EH烧结钕铁硼磁体具有优异的常温磁性能,同时表现出良好的温度稳定性。     

粘结稀土-钴的热稳定性

研究了一种聚合物粘结SmCo_5磁体和两种不同性能等级的环氧树脂粘结2∶17型稀土-钴磁体开路剩磁和退磁曲线随温度、保温时间和磁体退磁系数的变化。表明三种磁体开路剩磁随温度的可逆变化曲线之间没有大的差异。在75、100和125℃的时效过程中,沉淀硬化型磁体显示出比1∶5型磁体好的磁性稳定性,磁体的退磁系数越大,其开路剩磁不可逆损失也越大。在上述三种温度时效大约5000小时之后,1∶5型磁体的退磁曲线形状产生了较显著的变化。即使在75℃时效5131小时后,B/H=-2的1∶5型磁体的开路剩磁不可逆损失也高达28.5％,而尺寸相同的2∶17型磁体的开路剩磁不可逆损失却只有4.5～8.2％。     

富铈液相合金添加的再生烧结钕铁硼磁体研究

采用废旧的烧结钕铁硼电机磁钢作为研究对象(牌号33H),研究富铈液相合金添加量对再生烧结钕铁硼磁体的磁性能和微结构的影响。研究结果表明,在相同的烧结温度下,当未添加液相时,再生磁体密度很低;进一步提高烧结温度,磁体密度略有提高,但是磁体容易氧化、甚至开裂。随着液相合金的添加,再生磁体的密度不断提高,磁性能相应地明显改善,这说明液相合金具有明显的助烧结作用。但是当液相合金的添加量超过8%(质量分数)时,再生磁体的矫顽力降低,这可能因为过多的富铈液相添加使磁体中的富稀土相团聚,磁体微观结构变差。当液相合金添加量为5%,烧结温度为1080℃时,再生烧结钕铁硼磁体的磁性能最佳:剩磁Br达到11.67 k Gs,内秉矫顽力Hcj达到18.94 k Oe,磁能积(BH)max为33.1 MGOe。再生磁体的性能与原废旧磁钢相当,甚至略有提高,再生磁体具有优异的退磁曲线方形度(Hk/Hcj=0.972)。     

粘结剂和温压工艺对粘结钕铁硼材料性能的影响

为了获得高性能的粘结钕铁硼(NdFeB)磁体,对含偶联剂和粘结剂的钕铁硼粉体进行了温压压制实验。在70~110℃温度范围内,探索了温压压力、温度、粘结剂及其含量对粘结钕铁硼磁体的密度和性能影响。结果表明:含0.5%偶联剂和0.6%粘结剂(均为质量分数)的钕铁硼粉体的压制规律符合黄培云压制方程,压制模量为3.57 MPa,非线性指数为0.21;随着压力和温度的升高,粘结磁体的密度和最大磁能积先升高然后下降。当粘结剂含量大于1.0%(质量分数)后,磁体密度迅速下降;在相同的温度、压力和粘结剂含量下,加入半固体的E44粘结剂比加入E51和CYD粘结剂的磁体密度大。在温压温度为80℃条件下,获得了密度6.7 g/cm~3,磁能积104 kJ/m~3的粘结钕铁硼永磁材料。     

钴含量对烧结钕铁硼居里温度及磁性能影响规律研究

与烧结钐钴磁体相比,烧结钕铁硼稀土永磁具有优异的室温磁性能和力学性能,但其居里温度较低,只有310℃左右,限制了其在耐高温磁应用领域的使用推广。钴元素部分取代钕铁硼中的铁元素可以提高钕铁硼永磁体的居里温度,传统的钴添加方式会使磁体中形成铁钴软磁相,从而造成磁体的矫顽力大大降低。本文研究了不同钴添加量对钕铁硼磁体物相、居里温度和磁性能的影响规律,结合Al、Ga、Cu等元素对钕铁硼永磁体晶界相物相结构的协同调控作用,避免了钴元素取代铁元素过程中Fe-Co软磁相的产生。本研究制备的高钴含量钕铁硼磁体矫顽力高H_cj>28kOe,居里温度T_c>450℃,剩磁温度系数|α|20℃～100℃<0.078%/℃,矫顽力温度系数|β|20℃～100℃<0.55%/℃。     

烧结钕铁硼晶界扩散矫顽力增强机制研究

高矫顽力烧结钕铁硼磁体具备较强的抗退磁能力和良好的温度稳定性,是保障永磁电机长期安全运转的关键基础。传统制造技术需要在材料中加入大量重稀土元素以提升材料的矫顽力,然而,重稀土元素极为稀缺因而价格高昂,并且重稀土元素直接添加不可避免的会造成材料剩磁的明显下降。本文研究了烧结钕铁硼晶界扩散处理后磁体的微观组织结构变化规律和矫顽力增强机制,通过晶界富稀土相组成及分布的优化,材料矫顽力得到大幅提升,适合制造兼具高剩磁、高矫顽力的高性能钕铁硼永磁材料。     

稀土钴永磁体的剩磁温度系数简易测量方法

近几年来,稀土钴永磁材料在我国得到了发展。随着它的应用的日益广泛,迫切要求测定磁体的磁性温度系数。目前,国内通用的测定稀土钴永磁体退磁曲残的办法是:首先用强脉冲磁场磁化,然后在电磁铁中测量剩磁Br及其它各点。用这种方法,只能进行室温测量,若要求在升温条件下进行测量,是困难的。一九七二年,我所采用可控硅半周波脉冲磁场装置和铁轭测量稀土钴永磁体的Br值,然后在由磁铁中测量退磁曲线其它各点。这种方法不仅简单易行,数据较可靠,而且由于铁轭体积较小,有利于在升温条件下测量磁体的剩     

永磁电机用钕铁硼磁体性能参数测试与分析

针对稀土永磁电机用钕铁硼磁体热稳定性差,测试了45SH钕铁硼磁体在不同温度下的磁性能参数变化、磁通量损失、电阻率的变化;可以看出:磁体样品温度升高,矫顽力温度系数逐渐降低,剩磁温度系数在升高,拐点上升,磁通损失明显,材料的电阻和电阻率反而趋势增大,电导率趋势减小.结果表明:钕铁硼永磁电机中的永磁体磁性变低,电机的参数性能指标就发生改变,永磁体的温度稳定性对电机应用至关重要.     

退磁工艺对各向异性粘结NdFeCoB退磁效果的影响

分别研究了以聚四氟乙烯(PTFE)和环氧树脂(Epoxy resin)为粘结剂的各向异性粘结NdFeCoB取向成形后经不同次数的交流脉冲退磁后的表面剩磁Br,以及上述磁体再经过热退磁后的表面剩磁Br.发现两种磁体即使经过多次交流退磁也并不能将其完全退磁,因此必须对其进行热退磁.研究了热退磁对两种磁体的表面剩磁的影响,同时重点研究了热退磁温度和保温时间对以PTFE为粘结剂的各向异性粘结NdFeCoB的表面剩磁和矫顽力的影响.结果表明,在370℃保温10min,既可以保证退磁效果,又不至于引起磁体更多的热磁损失.     

Characterization of Microstructure and Magnetic Properties of NdFeB Magnet with Dy, Al and Cu Additions

A new alloy of Nd33.5Dy0.99Febal.Al0.52Cu0.1B1.15 (%, mass fraction) was fabricated by powder metallurgy. The effects of Dy, Al and Cu additions on the microstructure and magnetic properties of sintered NdFeB magnet were investigated. The additions of Dy, Al and Cu are effective to refine grains and improve coercivity. Moreover, suitable amounts of Dy, Al and Cu lead to a demagnetization curve with good rectangularity. It is found that the sintered NdFeB magnet has relatively high magnetic performance of Br=12.17kGs, jHc=13.52kOe and (BH)max=34.71MGOe. The sintered NdFeB sample was examined by magnetic force microscope which revealed the domain structures at the surface. It is revealed that the mean Nd2Fe14B grain size is significantly larger than the average scale of the magnetic contrast. An explanation about this is that most Nd2Fe14B grains in sintered NdFeB alloy are dominated with the muhidomain structures when the magnet is in thermally demagnetization state.     

成形工艺对粘结NdFeB磁体结构和磁性能的影响

在粘结NdFeB磁体模压成形过程中存在较大的压力损失，引起磁体密度分布不均匀，致使磁体密度减小。本文研究了压制压强、预压成形和压制方式等对粘结NdFeB磁体结构和磁性能的影响及机理。研究表明：随着压制压强提高，粘结NdFeB磁体的密度和磁性能显著增大；粒度配合、预压成形和双向压制等办法均可增大粘结NdFeB磁体的密度和磁性能；在适当的压制压强下，将粒度配合、预压成形及双向压制工艺结合，制备出密度达到6．5g／cm^3、磁能积达到104kJ／m^3的粘结NdFeB磁体。     

Microstructure and magnetic properties of(SmCo+FeCo)/NdFeB multicomponent nanocomposite magnets fabricated by HPTC with change in heating temperature and composition

We report the fabrication of bulk anisotropic(SmCo+FeCo)/NdFeB multicomponent nanocomposite magnets using high-pressure thermal compression(HPTC).The correlations among microstructure,magnetic properties,heating temperature and composition of the HPTC nanocomposite magnets were studied.The HPTC magnet made under variable temperatures(VT),with 19 wt% of FeCo phase,exhibits a maximum energy product of 32 MGOe,which is much higher than that(14 MGOe) for the HPTC magnet made under a constant temperature(CT).When the FeCo content increases to～23 wt%,the HPTC magnet made under VT still remains a high energy product of about 25 MGOe.With increasing NdFeB content,the(SmCo+FeCo)/NdFeB multicomponent nanocomposite magnets exhibit an enhanced magnetic anisotropy and coercivity.This work is beneficial to fabricating high-performance and low-cost permanent magnets for practical applications.     

Influence of Heat Treatment on Microstructures and Properties of Nd8Fe78B6Co4 Alloy

Melt-spun Nd8Fe78B6Co4 magnetic powders and their bonded magnets were prepared with the optimization of compositions and preparation techniques. The microstructure change of alloy NdFeB and the relation between microstructure and heat-treatment were studied. The heat-treatment temperature is 200～700 ℃. The as-cast structure of the alloy is typically amorphous. Different melt-spun speed and different heat treatment could result in different magnetic properties of NdFeB magnets. Magnetic properties of NdFeB increase with the addition of element Co. The magnetic properties of magnet alloy get the best when the melt-spun speed reaches 23～26 m·s-1, heat treatment temperature is 690 ℃ and time is 30 min.     

Anisotropic NdFeB/SmCoCuFeZr composite bonded magnet prepared by warm compaction process

Anisotropic NdFeB/SmCoCuFeZr composite bonded magnets were prepared by warm compaction process. The effects of adding SmCoCuFeZr magnetic powder on the properties of anisotropic bonded NdFeB magnet were investigated in this work. The results show that, both magnetic properties and temperature stability of the bonded magnet can be improved by adding fine SmCoCuFeZr magnetic powder. In the present study, the optimal content of SmCoCuFeZr magnetic powder was about 20 wt.%, in this case, the Br, Hcj, and(BH)maxof the NdFeB/SmCoCuFeZr composite magnet achieved 0.943 T, 1250 kA/m, and168 kJ/m~3, respectively.     

Effect of Particle Size and Distribution of Rapidly Quenching NdFeBMagnetic Powder on Magnetic Properties of PolymerBonded NdFeBPermanent Magnet

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Microstructure improvement related coercivity enhancement for sintered NdFeB magnets after optimized additional heat treatment

The microstructure, especially the Nd-rich phase and the grain boundary, in sintered NdFeB magnets plays an important role in magnetic reversal and coercivity mechanism. To better understand the effects of the microstructure on the coercivity, we investigated the microstructure and properties improvements of a commercial sintered NdFeB magnet after optimized additional heat treatment. The coercivity is enhanced from 1399 to 1560 kA/m. This enhancement has been explained in terms of the evolution of the grain boundary structure, and the formation of continuous thin layers of Nd-rich phase is important for high coercivity. The micromagnetic simulation together with the numerical analysis based on the nucleation model suggest that the reversed magnetic domains nucleate mainly at the interface of multi-junctions of Nd₂Fe₁₄B grains with high stray fields during the demagnetization process. Both improved anisotropy fields at grain boundaries and reduced stray fields at multi-junction Nd-rich phases contribute to the coercivity enhancement. This work has importance in understanding the crucial microstructure parameters and enhancing the obtainable properties for sintered NdFeB magnets.     

工艺参数对注射成形各向异性粘结NdFeB磁体性能的影响

研究了注射温度、模具温度、注射压力及注射速度对注射成形各向异性粘结NdFeB磁体的磁性能及力学性能的影响，并分析了其原因。结果表明：注射温度及模具温度对磁体磁性能影响较大，而注射压力则对磁体的抗压强度影响较大。在最佳的注射参数下，获得了最大磁能积和抗压强度分别为90kJ／m^3及130MPa的高性能粘结磁体。     

Preparation Technology and Performances of Zn-Cr Coating on Sintered NdFeB Permanent Magnet

Since appearing in1983,sintered NdFeB perma-nent magnet has been applied widely and become ani mportant basic material in high technology fields be-cause of its excellent magnet property,wide sources ofraw material and low price[1].Active phase such asNd-rich phase and B-rich phase in NdFeB permanentmagnet facilitated easy corrosion in corrosion medium,which weakenedits magnet property,andturnedit intopowder-like,non-usable product.So surface treatingfor anticorrosion was veryi mportant for…     

Magnetovisual method for monitoring thermal demagnetization of permanent magnets used in magnetostrictive actuators

The design and measuring potential of the latest generation of the magnetic scanner called Magscanner-Maglab System （MMS） was presented. It enabled the fast acquisition of 3D signals from magnetic sensors and their visualization as digitalized mag- netic images. This system was used for monitoring of a thermal demagnetization process of permanent magnets. The original method and measurement devices were capable for examination of magnetic, mechanical and thermal defects in cylindrical rods made of NdFeB and non-rare earth components. Effectiveness of the method and device was tested for the reference demagnetized magnet dedicated for magnetostrictive actuators.