Research and application of rare earth permanent magnetic materials
The application of rare earth permanent magnetic materials has become increasingly widespread, and has become an important symbol of the development level of modern civilized society, and has played an important supporting role in the successful implementation of “Made in China 2025”. Among the proven rare earth reserves, my country ranks first in the world and is known as the kingdom of rare earths. This has laid a solid foundation for my country to vigorously develop the rare earth permanent magnet industry in the future. The emergence of rare earth permanent magnet materials has played a positive role in promoting industrial progress, especially in the motor industry and office automation. 
Development of rare earth permanent magnetic materials
Table of Contents
- Development of rare earth permanent magnetic materials
Study on rare earth permanent magnetic materials
- Technological progress of rare earth permanent magnet materials 
- Future research trend of rare earth permanent magnet materials 
- Application of rare earth permanent magnetic materials
Rare earth permanent magnetic materials are a kind of permanent magnetic materials based on the intermetallic compounds formed by rare earth metal elements re (SM, Nd, PR, etc.) and transition metal elements TM (Fe, Co, etc.). The rare earth permanent magnetic materials developed by rare earth transition metal compounds have excellent permanent magnetic properties, and are a kind of permanent magnetic materials with the highest coercivity and the largest magnetic energy product at present. 
Alnico permanent magnet appeared in the late 1940s, ferrite permanent magnet appeared in the 1950s, the first generation of rare earth permanent magnet SmCo5 was developed in the 1960s, and the second generation of rare earth permanent magnet Sm2Co17 was successfully developed in the 1970s. In 1983, Sumitomo special metal’s Mr. satokawa of Japan and general motors of the United States respectively developed NdFeB, which is the third generation of rare earth permanent magnet material.
Due to its excellent comprehensive magnetic properties, the third generation of rare earth permanent magnet material NdFeB is widely used in various pillar industries and high-tech industries such as computer, communication information, medical treatment, transportation, audio equipment, office automation and home appliances.
Since the beginning of this century, the global Nd-Fe-B industry has continued to grow in large volume driven by China. During the 15 years from 2002 to 2017, the annual average growth rates of sintered Nd-Fe-B production in China and the world were 17.8% and 14.5% respectively, and the annual average growth rates of bonded Nd-Fe-B production were 10.1% and 5.6% respectively. 
Study on rare earth permanent magnetic materials
Technological progress of rare earth permanent magnet materials 
In recent years, sintered Nd-Fe-B technology has been developing continuously, and the comprehensive performance of magnets has been steadily improved. With the increasingly wide application of sintered Nd-Fe-B in high-performance motors, magnets with high magnetic energy product and high working temperature have become the core goal of research and development. On the other hand, in order to improve the balance of rare earth resources and reduce the cost of magnets, high abundance magnets have also become the core goal of research and development Color is another important R & D goal. New technology is mainly to achieve these goals.
① Grain boundary diffusion technology
Grain boundary diffusion refers to the formation of (nd, Dy, TB) 2fe14b solid solution by introducing heavy rare earth elements (Dy or TB) into the surface of the magnet, and then making heavy rare earth atoms diffuse along the grain boundary through heat treatment, and replacing the original nd in the surface layer of the main phase grains. The center of the main phase grains is not affected too much. Therefore, the magnetic crystal anisotropy field on the surface layer of the grains is enhanced, and the intrinsic coercivity is increased, Compared with the traditional alloying element addition method, the grain boundary diffusion method can obtain high coercivity magnets with lower Dy and TB heavy rare earth content.
② Grain boundary control technology
Grain boundary control is another effective way to improve the coercivity. By adjusting the formula and process, it is expected to reduce the ferromagnetism of grain boundary phase or change it into non ferromagnetism, so as to better reduce or remove the magnetic coupling between grains, and further improve the intrinsic coercivity on the basis of the existing level.
③ Dual main phase technology
Since the price of rare earth raw materials fluctuated greatly in 2011, La, CE and mixed rare earth have attracted people’s attention again. Comparing the intrinsic magnetism of r2fe14b, when R is high abundance La, CE or Y, the saturation magnetization MS, magnetocrystalline anisotropy field HA and Curie temperature Tc are lower than Nd2Fe14B, so the magnetism of the magnets obtained by conventional element substitution method will inevitably decline On the one hand, when CE is added to Nd2Fe14B alloy instead of Nd, CE ions show mixed valence state of + 3 and + 4, which directly affects the phase composition and microstructure of sintered magnets and damages the intrinsic coercivity. However, the practical sintered magnets with high abundance can still be prepared by specific methods.
④ Grain refinement technology
Grain refinement is another important way to improve the coercivity. According to the micromagnetic simulation of sepehri Amin et al, decreasing the grain size can reduce the stray magnetic field, that is, it can reduce the local effective demagnetization factor Neff, so as to improve the intrinsic coercivity HEJ (HEJ = α ha neffms, α is the microstructure parameter). The work on grain refinement includes reducing the grain size of the rapid solidification (SC) alloy sheet, extracting the magnetic field In this paper, the methods of making powder by HDDR combined with HD and JM, changing the way of grinding or changing the medium from nitrogen to helium, controlling the process of oxygen free / low oxygen, low temperature multi field sintering and so on are introduced.
Bonded rare earth permanent magnet material is an indispensable branch in the field of permanent magnet materials. Bonded magnets play an important role in precision motors and sensors with the advantages of good consistency of magnetic properties, high dimensional accuracy, complex shape, low eddy current loss, suitable for multipole magnetization (especially multipole magnetization ring), and easy integration with metal / plastic parts. Bonded rare earth permanent magnets Isotropic bonded Sm-Fe-N magnets and anisotropic bonded rare earth magnets are being developed.
① Isotropic magnetic powder and bonded magnet
Bonded magnet is a composite system composed of magnetic powder and binder. Isotropic Nd-Fe-B magnetic powder prepared by rapid quenching is the main force of bonded rare earth permanent magnet market.
② Anisotropic magnetic powder and bonded magnet
Anisotropic bonded rare earth permanent magnet is an important branch which has a long history but needs to be developed urgently. The traditional bonded SM co magnet is anisotropic, and it is still in production. In the field of anisotropic bonded rare earth permanent magnet, the underdeveloped magnet manufacturing technology seriously restricts its development.
③ Manufacturing bonded rare earth magnet with additive
In recent years, 3D printing technology has been paid close attention and developed rapidly in many fields. Using 3D printing to prepare bonded magnets can not only deal with peculiar shapes, but also obtain special structures or properties that can not be achieved by conventional preparation methods.
Hot pressed / hot deformed NdFeB
Nanocrystalline magnetic powder (such as rapidly quenched Nd-Fe-B magnetic powder) can be prepared into isotropic compact magnet (mq-ii magnet) and anisotropic compact magnet (mq-iii magnet) by hot pressing / hot deformation process.
The high temperature resistance of sintered SmCo magnet has always been an important direction of research and development work. At present, the main aim is to improve the coercivity of the magnet by adjusting the composition and optimizing the process conditions, so as to improve the service temperature of the magnet and maintain high magnetic properties.
Future research trend of rare earth permanent magnet materials 
Development of bonded magnets with high magnetic energy product
Rare earth permanent magnet materials are basically NdFeB based materials, which can be divided into two categories: sintered magnet and bonded magnet. NdFeB sintered magnet is anisotropic and full density magnet, and its application is gradually expanding. However, NdFeB Bonded magnet is isotropic, and the shortcomings of NdFeB Bonded magnet are increasingly prominent. Firstly, its magnetic powder is isotropic In order to fully meet the needs of the current stage, the maximum energy product is relatively low. Secondly, the molding process also has great limitations, that is, NdFeB fast quenched magnetic powder is mainly used to make compression bonded magnets, but its production proportion is very low. With the requirements of the development trend of electrical miniaturization, the development of bonded magnets with high energy product has become a new demand direction of the market.
Promote the development of high performance anisotropic rare earth bonded magnets
In order to meet the development requirements of low-carbon economy, the development and research of high-performance anisotropic rare earth bonded magnets has become an important research issue of social development. There are two ways to develop new anisotropic rare earth bonded magnets in the world: one is to develop new materials, study new rare earth iron nitride permanent magnet materials, and manufacture single crystal anisotropic magnetic powder; the other is to develop new technology To manufacture textured Nd-Fe-B anisotropic magnetic powder, including preparation of Nd-Fe-B anisotropic magnetic powder and hot extrusion anisotropic magnetic powder.
Promote the research and development of nano rare earth permanent magnet materials
In the research and development of rare earth permanent magnetic materials, rare earth materials should be combined with nanotechnology. By combining the small size effect, quantum effect, surface effect and interface effect of nano materials with the unique electronic layer structure of rare earth elements, nanocrystalline NdFeB magnetic powder is prepared by a new processing technology, which can reduce the sintering temperature and improve the quality of products Because of its higher magnetic energy product, good shape freedom and high dimensional accuracy, NdFeB magnets have become the research focus of major NdFeB permanent magnet production companies and have broad market prospects.
Application of rare earth permanent magnetic materials
Rare earth permanent magnetic materials are characterized by light weight, small size, strong magnetism, high stability and low cost. So they have been widely concerned since they were invented. At present, rare earth permanent magnetic materials can be seen in digital products, machine tools, automobiles and mechanical equipment. The use of rare earth permanent magnetic materials improves the high performance and stability of products, and reduces the cost The product cost is reduced.
Application of rare earth permanent magnet materials in motor 
Motor is a kind of electrical mechanical equipment which uses magnetic field as the medium of transmission for energy conversion between electrical energy and mechanical energy. Generally speaking, magnetic field can be generated by current or permanent magnet. The density of general permanent magnet is relatively equal and the magnetism is limited, so the energy that can be converted is also limited. It can only be used to manufacture some small motor equipment. However, rare earth permanent magnet is widely used The use of magnetic materials in mining machines can produce a strong magnetic field, and can achieve continuous and permanent magnetic field transmission without the help of external force. Therefore, rare earth permanent magnet materials can be used to manufacture large-scale motor equipment and precision motor equipment. At present, rare earth permanent magnet motors have been widely used in China, covering aerospace, national defense equipment and large aircraft Electrical manufacturing, medical devices, automobile, production and other fields, its manufacturing scope almost covers the entire motor industry.
The characteristics of rare earth permanent magnet motor include:
- ① small volume and light weight. This can significantly reduce the overall appearance of motor equipment, make its application more widely, and bring great convenience to the production, transportation and installation of motor;
- ② strong performance and strong stability. It provides favorable support for the safe operation and efficient production of equipment and machinery;
- ③ high efficiency In general, the average power saving rate of rare earth permanent magnet motor in operation is about 10% higher than that of ordinary motor. Some special rare earth permanent magnet motors can increase the power saving rate by up to 15% ~ 20%. At the same time, rare earth permanent magnet motors can also realize variable speed regulation through the function of stepless frequency conversion, improve the operation efficiency and reduce energy consumption.
Application of rare earth permanent magnet materials in information technology 
The main function of permanent magnet materials is to provide a magnetic field for various devices or devices. It is usually used as a rotor in the rotating machinery of energy conversion, and as a constant magnetic field source in sensors, traveling wave tubes, sound horns and other devices and devices. In the information industry, permanent magnet materials have been widely used.
Rare earth permanent magnetic material is a very important magnetic functional material for information industry. It has a close relationship with modern information industry, especially “three networks” (telecommunication network, television network, Internet) and all aspects of smart grid. Rare earth permanent magnetic material is even essential in some fields of information industry.
Rare earth permanent magnet materials are widely used in all walks of life with its huge advantages. The use of rare earth permanent magnet greatly promotes the development of permanent magnet equipment and devices to miniaturization and integration, so it is widely used in wind power generation, new energy vehicles, consumer electronics, air conditioning, high-end equipment and many other fields. In the future, the development and utilization of rare earth permanent magnet materials in China should not only strengthen the research on high-performance neodymium The research, development and application of iron boron permanent magnet materials should strengthen their own integration, continuously improve the management and technical level, and maintain the initiative in the process of rare earth industry transferring to China. At the same time, we should pay close attention to and track the world’s new research and development trends of high-performance permanent magnet materials, and invest appropriate human and material resources in the scientific research and development of new materials, so as to make our country in the high-performance industry It can occupy a place in the advanced ranks of permanent magnet research and development, and maintain sustainable development in the field of high-performance permanent magnet materials.
Source: China Permanent Magnet Manufacturer – www.rizinia.com
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