NdFeB magnetic material is the third-generation of rare earth permanent magnet material based on intermetallic compound Nd2Fe14B. Its main components are iron (63.9-68.7%), rare earth element neodymium (29-32.5%) and boron (1.1-1.2%). The main manufacturing processes include smelting, pulverizing, pressing and orientation, sintering, machining, coating and magnetizing.
In an environment of suitable temperature, humidity and no existing external magnetic field, radiation and other factors affecting magnetic performance, the magnetic properties of neodymium magnet material will not suffer much loss. NdFeB magnet has the highest magnetic properties and the best overall magnetic performance among all modern permanent magnet materials. The magnetic properties of NdFeB magnets can help realize important functions such as the conversion of electrical signal and the conversion of electrical-mechanical energy. It also contributes to the miniaturization of electronic instruments and communication equipment. Neodymium magnet is called “the supreme leader of all permanent magnets”.
Magnetic materials refer to those materials that can directly or indirectly generate magnetism from transition elements such as iron, cobalt, nickel and their alloys. Magnetic materials can be divided into soft magnetic materials and permanent (hard) magnetic materials according to how easy or difficult it is to demagnetize the magnet after magnetization. According to production process, they can also be divided into sintered magnets and bonded magnets.
The most important indicators of magnetic materials are maximum energy product (BH)max and coercivity Hc. High magnetic energy product and high intrinsic coercivity represent that the magnetic material required to produce the same magnetic strength is smaller in size, lighter in weight, more resistant to demagnetization and more efficient in energy. Maximum energy product, coercive force and remanence are three main indicators of the magnetic properties of a magnetic material. In addition, the maximum operating temperature and Curie temperature are used to indicate the temperature characteristics of a magnet. The higher the maximum operating temperature and the Curie temperature, the better the temperature stability of the magnet.
Rare earth permanent magnet materials have been developed to the third generation – Nd2Fe14B (Neodymium-Iron-Boron) magnet. Rare earth permanent magnet materials can be divided into four generations according to the development stages: after AlNiCo permanent magnet and ferrite permanent magnet material, the first and second generation of rare earth permanent magnet materials SmCo5 and Sm2Co17 emerged one after the other. NdFeB magnet is the third generation of rare earth permanent magnet successfully developed and commercialized in 1980s. The fourth-generation represented by rare earth iron nitrogen (R-Fe-N) and rare earth iron carbon (R-Fe-C) are still in the research and development stage.
Sintered NdFeB magnet has high magnetic energy product, remanence and intrinsic coercive force. Its maximum magnetic energy product is about 2 times that of the first-generation rare earth permanent magnet SmCo5, 1.5 times that of the second-generation rare-earth permanent magnet Sm2Co17. Its intrinsic coercivity (Hcj) is about twice that of Sm2Co17. The magnetic properties are 1.3 times that of SmCo5 and 1.2 times that of Sm2Co17.
According to manufacturing process, NdFeB magnet can be divided into three groups: sintered NdFeB magnet, bonded NdFeB magnet, and hot-pressed NdFeB magnet. The main feature of sintered and hot-pressed NdFeB magnets are excellent magnetic properties, while the advantages of bonded NdFeB magnets are tight tolerance, possibility in complex shape, flexibility in magnetization, and high material utilization. However, the magnetic performance of bonded NdFeB magnet is far lower than that of sintered NdFeB magnet, and therefore it has a limited application scope. In terms of hot-pressed NdFeB magnet, due to its complex production process and high processing costs, its current output is relatively small and has not yet formed a complete industry.
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