Preparation Of Melt-spun Yttrium-iron-based Permanent Magnetic Materials And The Mechanism Of Magetic Hardening

Since the Nd-Fe-B-type permanent magnets was invested and widely used in modern industry, the consumption of rare earth (RE) elements, such as Nd,Pr and Dy, has been increasing quickly while the production of other RE elements such as La,Ce and Y exceeds their consumption significantly. This article mainly studies the magnetic properties of yttrium-iron-based permanent magnets. The sense of our study is to expand the application of yttrium and to keep the RE industrial development in balance.The main content of this article is the preparation of the yttrium-iron-based permanent magnetic alloys.The compositions of alloys in our experiments are designed systematically based on the tenary equilibrium phase diagram. For different compositions, we discuss the difference of magnetic properties and phase composition between the samples with different process parameter such as the wheel velocity, annealing temperature and annealing time. We have investigated the phase composition, magnetic reversal prcess and micro structures of the yttrium-rion-boron alloys through XRD, VSM and STEM. The mechanism of the magnetic hardening in the alloys has been researched.(1) The optimal permanent magnetic properties obtained in yttrium-iron-boron alloys is of (BH)max=5.2MGOe, Hcj=5.7kOe (in the composition of Yi6Fe69B15 quenched at 35m/s and annealed at 700℃ for 10 minutes)and Br=6.1 kGs(in the composition of Y16Fe78B6 quenched at 35m/s and annealed at 700℃ for 10 minutes).(2) The anisotropy field of Y-Fe-B alloys is mainly derived from the hard magnetic phase Y2Fe14B thus the extent of Y2Fe14B crystallization influence the magnetic properties significantly. For the composition series of YmFebalBn, the effective composition range is of 13≤m≤19,6≤n≤18. The main phase structure of samples quenched at the wheel velocity exceeds 35m/s is amorphous and transform into nanocomposite after heat-treaments. The optimal process of heat treatments is annealed at 700℃ for 10 minutes based on the data of TG/DSC and magnetic properties.(3) When the content of yttrium in the alloy is 16%(atomic percent), the series of alloys have a relative better properties. Increase or reduce the content of yttrium will produce YFe2 or YeFe23 which leads to the decay of permanent magnetic properties.(4) The highest coercivity appears in the composition of Y16Fe69B15 and in the composition range of Y13-16Feba1B6-18 have a coercivity exceeds 3kOe which is practical for permanent magnets. The high coercivity in Y16Fe69B15 comes from the pinning effect of grain boundary phases which is identified as YFe2B2.Besides the annealing time of 10 minutes leads to a optimal size of grain boundary phase.(5) There is an obvious exchange-coupling effect in the Y16Fe78B6 alloys. The grain sizes of alloys prepared by amorphous-annealing after quenching. The change of the dealing process leads to the homogeneity of grain sizes decrease as well as the effective exchange-coupling. Amorphous-annealing after quenching can also avoid the growth of a-Fe grain formed in Y16Fe78B6.The research content of this article focuses on the relationship between compositions, process parameters and magnetic properties. We have evaluated the permanent magnetic properties of yttrium-iron-boron alloys and figure out the mechanism of the magnetic hardening. We find some possible ways to improve the properties of Y-Fe-B alloys during our experiments including enhancement of exchange-coupling and domain-pinning effect, elements addition to improve the anisotropy field, the control of the microstructure and so on. According to our research it is possible to develop a new kind of practical permanent magnets based on yttrium-iron-boron alloys.