| In order to improve the magnetic properties of nanocomposite Nd2Fe14B/α-Fe permanent magnets by optimizing microstructure, with the problem existing in the development of nanocrystalline composite magnets, nanocomposite Nd2Fe14B/α-Fe permanent magnets are prepared by rapidly quenching, post heat treatment and mould pressing in this paper. The phase composition, microstructure and crystallization behavior are studied by X-ray diffraction (XRD), differential thermal analysis (DTA), transmission electron microscopy (TEM), and atomic force microscopy (AFM). Effect of preparation parameters and component on microstructure and magnetic properties of nanocomposite permanent magnets have been investigated. The physics models for the relationship between microstructure and preparation parameters and component, and the relationship between magnetic properties and microstructure have been established. In order to research the influence of multi-factors on magnetic properties of Nd-Fe-B permanent magnets, uniformity design experiments are adopted. Experimentation datum are dealed with by statistical analysis software (SAS), and regression equations between component and magnetic properties of Nd-Fe-B permanent magnets are obtained using step by step regression. And the relationship between component and magnetic properties is established by artificial neural network(ANN) predicting model.The quenching speed plays an important role in the crystallization behavior, phases transformation and microstructure of as-spun alloy, and consequently it influences the magnetic properties. For Ndio.s(FeCoZr)83.4B6.1, at lower quenching speed, the amount of nuclei increases. It is easy to grow coarsely for crystallized compound, and result in worsen the magnetic properties. While at the higher quenching speed, the lower alloy crystallinity is, and the smaller nucleation center the as-spun alloy has during the crystallization process. As a result, the magnetic properties are low because of an inhomogeneous microstructure, a great inner stress and coarse grain of α-Fe. When the quenching speed is 28m/s, the crystallinity of as-spun alloy is about 20%, which has a certain amount of crystallized compound as the nucleation center during the crystallization process and increases the nucleation rate. The nucleation of a solid precipitate from the matrix occurs most easily on boundary which prevent the growth of grain and the amount of nuclei is largest. Thus a fine and homogenous microstructure and excellent combination of magnetic properties are obtained.When the crystallization temperature is low, the magnetic phases precipitate incompletely, and amorphous phases existing in the alloys. And thereby the exchange coupling interaction is weak and the magnetic properties are low. When the crystallization temperature is high, the exchange coupling interaction is weak due to the coarse grain of α-Fe, and the magnetic properties such as Br and (BH)m degraded. But Hcj increases with the heightening the crystallization temperature, as a result of the amount of the hard magnetic phase Nd2Fe14B with high anisotropy of magnet crystal increasing. Magnetic properties, such as Br, Hcj and (BH)m, increase with the crystallization time increasing at first, and then decrease, that is to say it exists a maximum. It has been determined that, compared with the conventional heat treatment, unconventional heat treatment can promote crystallization of melt-spun NdFeB powder from amorphous phase, decrease the crystallization temperature and shorten the crystallization time. Moreover unconventional heat treatment can refine grains, enhance the exchange coupled interaction between the grains, and increase the magnetic properties. As a result, the optimal magnetic properties ofNd10.5(FeCoZr)83.4B6.1 (Br=0.684T, Hcj=685 kA/m, Hcb=439kA/m, (BH)m=79kJ/m3) are obtained after dynamic crystallization heat treatment at 670 D for 10min.With the increase of atom percent of Nd for Ndx(FeCoZr)93.9-xB6.1 alloy, the volume fraction of soft magnetic phase and the remanence Br decrease. When atom percent of Nd is 9.5, Br reaches the maximum, which is about 0.693T. The coercivity increases linearly with the increase of atom percent of Nd, and reaches the maximum when atom percent of Nd is 11.8, Hcj=802kA/m and Hcb=439kA/m. (BH)m is affected by Hcj, Br and the squareness of demagnetization loop and is gradually improved first, and then decreased with the increasing of the Nd content,has a parabola-shaped tendency.Increasing the B content or Zr content can promote the formation of amorphous phases. The grain size is reduced and the microstructure can be improved by adding B element or Zr element. But if the content of B exceeds a certain level, nonmagnetic phase Nd1.1Fe4B4 occurs during crystallization of the alloys, and increase with the increase of atom percent of B. As a result, the exchange coupled interaction between the grains becomes weak and the magnetic properties decrease with the B content increasing. The optimal magnetic properties of Nd10.5(FeCoZr)89.5-yBy are obtained when y =6.1. Zr addition promotes the formation of Fe2Zr with high melting point during the process of crystallization. The grain size is reduced by adding Zr element. Moreover, Zr restrains the formation of metastable phases, e.g. Nd2Fej7 and Nd2Fe23B3 during crystallization of the alloys. Zr addition is a very effective way to increase the coercivity, improve the squareness of demagnetization loop, and increase the energy product. The optimal magnetic properties of Nd10.5(Fe,Co)83.4-zZrzB6.1 are obtained when z =2. With the increase of atom percent of Co for Nd10.5(Fe,Zr)83.4-mComB6.1 alloy Br increases and coercivity (Hcj,Hcb) decreases gradually, and (BH)m first raises and then drops, that is to say it exists a maximum.Regression equations between component and magnetic properties of Nd-Fe-B permanent magnets are obtained using uniformity design experiments method andstep by step regression means. Analysis of variance (ANOVA) shows that the regression models are creditable, and it can be used to discussed the influences of multi-factor interaction on alloy magnetic properties. The results indicate that Co have advantageous effects on increasing Br, and Zr, B and the interaction between the two alloying elements have disadvantageous effects on increasing Br. The affections of Nd, Zr and B content on coercivity Hcj assumed linear increase gradually, however the affection of Co assumed the quadratic nonlinear progressively decreasing regularity. Maximal energy product (BH)m presents a parabola-shaped tendency with the increase of atom percent of Nd. Both B and Zr affect (BH)m, and there exists certain interaction between this two alloying elements.The predicting model is established by using artificial neural network to simulate the relationship between alloy composition and magnetic properties. The model has good precision and low relative errors. 2-dimension curves, 3-dimension figures and contour lines of content-properties are obtained by the ANN model. The influences of single element or the interaction among elements on magnets magnetic properties are respectively discussed according to the curves ploted by ANN model. Simulation result shows that the coercivity Hcj can be obviously improved and the remanence Br can be reduced by increasing Nd or Zr content; Co and B have advantageous effects on increasing Br and disadvantageous effects on increasing Hcj; influence of alloying elements on Hcj and Br are inverse; and the interaction among the alloying elements play an important role in megnetic properties of NdFeB magnets.The nanocomposite Nd2Fe14B/α-Fe permanent magnets with high magnetic properties, with Br=0.69T, Hcj = 800kA/m, (BH)m=83kJ/m3, are obtained by ANN model, which corresponds to the typical bonded magnets of MQP.
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