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Effect of Process and Trace Elements on the Properties of NdFeB

High performance neodymium iron boron magnet, sintered NdFeB neodymium magnet, microstructure, hard magnetic properties, grain size, high coercivity, process, addition of trace elements, magnetic energy product, permanent magnet material, rare earth permanent magnet, magnetic domain structure , magnet coercivity, alloy, main phase, application, temperature, microstructure, sintered magnet, orientation, permanent magnet material has become a modern science and technology, such as computer technology, information technology, aerospace technology, communication technology, transportation technology, office An important material basis for automation technology, home appliance technology, and human health and health care. The commonly used permanent magnet materials are mainly ferrite, aluminum nickel cobalt and rare earth permanent magnets. The rare earth permanent magnet materials include samarium cobalt and neodymium iron boron, among which NdFeB neodymium has a record high remanence, high coercivity and high magnetic energy product, and is called a new generation rare earth permanent magnet or a third generation rare earth permanent magnet. NdFeB neodymium magnets can be divided into sintered NdFeB neodymium magnets, bonded NdFeB neodymium magnets and thermally deformed NdFeB neodymium magnets according to their preparation processes. The magnetic energy product of sintered NdFeB neodymium magnets is high. At present, the international laboratory research level has reached 444kJ/m<'3>(55.8MGOe), and industrial production has reached 414kJ/m<'3>(52MGOe), but most of China NdFeB neodymium production enterprises, due to outdated production equipment and backward process technology, result in low product performance (magnetic energy product is generally around 278-320kJ/m<'3> (35-40MGOe)), and the stability and consistency of performance are poor. It has not been able to enter the mainstream application field of NdFeB neodymium magnets. Sintered NdFeB neodymium permanent magnet materials have been rapidly popularized and applied for their high magnetic energy product, low cost and good processing performance. With the expansion of its application fields, the requirements for its comprehensive performance are getting higher and higher. In particular, the application environment of NdFeB neodymium permanent magnet motor is becoming more and more demanding, and the demand for high heat resistant sintered NdFeB neodymium magnets is also More and more intense. High coercive sintered magnets, if combined with a low temperature coefficient, can be used at higher temperatures, especially for sintered NdFeB neodymium magnets that can be used at temperatures above 200 °C. The wider the coming. This is because although the Sm-Co magnet can work at temperatures above 300 ° C, it is expensive because of the need to add a large amount of strategic element Co. Therefore, in the temperature range of 200 to 300 ° C, sintered NdFeB neodymium magnets have great advantages. The first is its

The magnetic properties are high, generally the maximum magnetic energy product is greater than 30MG0e, and the magnetic energy product of the Sm-Co magnet is much lower. Secondly, the sintered NdFeB neodymium magnets do not contain or contain only a small amount of strategic elements such as Co and Ni, and the price is lower than that of Sm-Co, and the overall cost performance is much higher. Moreover, the sintered NdFeB neodymium magnet has good mechanical properties and can be processed better than the Sm-Co magnet, thereby reducing the reject rate and improving the production efficiency. Therefore, the development of high coercivity sintered NdFeB neodymium magnets is an important direction for competition in the future. The hard magnetic properties of NdFeB neodymium magnets mainly depend on the Nd<,2>Fe<,14>B(2:14:1) main phase. Adjusting the main phase composition of the magnet can improve the internal magnetic parameters and optimize the microstructure of the magnet crystal to improve the macro hard magnetic properties. We adopt advanced production equipment and adopt a new magnet preparation process. By adjusting process parameters, optimizing composition formula and adding trace elements, the hard magnetic properties of the magnet can be greatly improved. Our main research work is as follows:

(1) Nd<,33.5>Dy<,0.99>Fe<,bal> was prepared by the traditional powder metallurgy method. Al<,0.52>Cu<,0.1>B<,1.15>(wt%) alloy magnets, the effects of adding trace elements Dy, Cu and Al on the microstructure and magnetic properties of the magnets were investigated, and high coercivity magnets were developed. . The results show that the addition of Dy, Cu and Al by conventional process is particularly effective for improving the coercive force of sintered magnets. The addition of Dy not only increases the anisotropy field of the magnet, but also refines the crystal grains, inhibits the precipitation of soft magnetic a-Fe in the alloy, effectively improves the microstructure of the magnet, and significantly increases the coercive force of the magnet. There are two reasons for adding Cu to increase the coercivity of the magnet:

One is that Cu enters the main phase and occupies the J<,2> crystal position, which reduces the plane anisotropy, which is beneficial to increase the uniaxial anisotropy field and improve the coercive force of the magnet.

On the other hand, Cu makes the crystal grains fine, and the specific surface of the crystal grains increases, and for the high-performance magnets with a low antimony composition, the distribution of the enthalpy-rich phase is required to be more uniform. The special wettability of Al plays a good role in wetting at grain boundaries, and a new Al-rich phase is formed at the grain boundaries, which makes the grain boundaries clear and more effectively reduces the exchange between grains. The demagnetization of the coupling increases the coercivity.

The magnetic domain structure was analyzed by magnetic force microscope. It can be found that the width of the magnetic domain is much smaller than the average grain size, indicating that the sintered NdFeB neodymium grains are almost multi-domain structures in the thermal demagnetization state.

(2) Nd<,31.0>Dy<,1.08>Fe<,bal>.Nb<.0.5>Al<, was prepared by the Hydrogen Decretitation (HD) process and the Jet Milling (JM) process. 0.34>B<,1.1> (wt%) magnet. The effects of hydrogen treatment crushing and air milling process conditions on the microstructure of the magnet were studied. The results show:  

a: Using this process, the alloy of the magnet can be distributed to a composition close to the main phase Nd<,2>Fe<,14>B, and the main phase crystal grains are fine, the enthalpy phase distribution is uniform, and the soft magnetic a- avoidance is avoided. Fe phase. The microstructure of the alloy prepared by this process satisfies the requirements of high performance NdFeB neodymium magnets for alloys, and opens up a new way for the preparation of high performance NdFeB neodymium magnets. The addition of some alloying elements can improve the magnetic properties of sintered NdFeB neodymium.

 b: Nb is added to the alloy to form NbFe and Nb<,2>Fe<,3> two kinds of compounds, which hinders the precipitation of a-Fe to some extent and refines the grains of the sintered body. Moreover, the addition of Nb makes the grain shape of the sintered magnet more regular and the size tends to be uniform, and the intergranular Nd-rich phase distribution is more uniform. Nb is mainly in the rich phase, sometimes associated with Dy, and Dy mainly enters the main phase. When Dy<,2>O<,3> is added during the milling, the coercive force of the sintered body can be improved, and the growth of the particles can be hindered. By observing the magnetic domain, the causes of magnetic domain generation and the domain morphology are analyzed. The crystal morphology is related to the corresponding magnetic domain structure. It is found that the composite addition of Dy, Nb and Al makes the magnetic domain structure of the magnet clearer. Magnetic texture has been formed. It also explains the relationship between magnetic domain structure and magnetic properties. We also studied the relationship between pulsed magnetic field and degree of orientation.

The results show that the repeated pulse magnetic field orientation process is very beneficial to improve the orientation of the compact.

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