sintered NdFeB permanent magnets

We all know that the main raw materials of sintered NdFeB permanent magnets are neodymium, iron, and boron. In addition, many other elements are added to the raw materials. These elements play different roles in the magnets. Manufacturers often design product formulas based on user needs. The raw material formula can be said to be top secret information of each manufacturer.   The dozen or so elements in sintered NdFeB are like the various seasonings we add to a delicious dish. It is precisely because of the scientific and regular combination of these elements with different intrinsic characteristics and functions that we have achieved various grades and properties of NdFeB. Understanding the significance of each element is of great significance to our better understanding of the performance and manufacturing costs of different grades.   For easier understanding, we can divide the constituent elements of NdFeB into three categories: First, the main elements RE (Ce, Gd, Nd, Dy, etc.), Fe, and B, which are primarily responsible for forming the RE2Fe14B primary phase grains. Second, minor elements such as Al, Co, Ga, and Zr which are primarily responsible for optimizing the coating of the grain boundaries around the primary phase grains. Third, impurity elements, such as carbon and oxygen, are inevitably introduced from raw materials and during production.   The schematic diagram of NdFeB element types is shown below:     During use, we must carefully consider the actual content of each batch as specified in the quality inspection form. Each element in NdFeB magnets has its own unique properties, such as:   1. The introduction of La and Ce reduces the magnet's remanent magnetization (Br) and coercivity (Hcj), but their low cost can reduce costs. 2. Re-element Fe-B (REFeB), composed of pure Nd replacing PrNd, has a very high saturation magnetization and can be used to produce ultra-high remanence magnets. 3. The introduction of Tb can significantly increase the magnet's Hcj, but its cost is extremely high. 4. Gd is relatively inexpensive, and the REFeB it forms has the highest Curie temperature, making it suitable for producing high-temperature-resistant magnets, but it significantly reduces the Br content.   By having an in-depth understanding of the characteristics of the above elements and figuring out the influence of various elements on the sintering process, sintering density, aging process, and product performance, we can produce NdFeB products with high cost performance.

In the application field of NdFeB magnets, there is a close relationship between the magnetism and temperature. When the temperature of the magnet exceeds a certain threshold, permanent demagnetization will occur, and the maximum operating temperature that different grades of NdFeB magnets can withstand varies.   Curie temperature   When studying the effect of temperature on magnetism, "Curie temperature" is a key concept. The naming of this term is closely related to the Curie family. In the early 19th century, the famous physicist Pierre Curie discovered in his experimental research that when a magnet is heated to a certain temperature, its original magnetism will completely disappear. Later, people named this temperature Curie point, also known as Curie temperature or magnetic transition point.   From a professional definition, Curie temperature is the critical temperature at which magnetic materials achieve the state transition between ferromagnetic and paramagnetic materials. When the ambient temperature is lower than the Curie temperature, the material exhibits ferromagnetic properties; when the temperature is higher than the Curie temperature, the material turns into a paramagnet. The height of the Curie point mainly depends on the chemical composition and crystal structure characteristics of the material.   When the ambient temperature exceeds the Curie temperature, the thermal motion of some molecules in the magnet intensifies, the magnetic domain structure is destroyed, and a series of ferromagnetic properties such as high magnetic permeability, hysteresis loop, magnetostriction, etc. associated with it will disappear, and the magnet will undergo irreversible demagnetization. Although the demagnetized magnet can be re-magnetized, the required magnetization voltage is much higher than the first magnetization voltage, and after re-magnetization, the magnetic field strength generated by the magnet is usually difficult to restore to the initial level.   Material Curie temperature Tc (℃) Maximum operating temperature Tw (℃) NdFeB 312 230   Working Temperature   Refers to the temperature range that the neodymium magnet can withstand during actual use. Due to the differences in thermal stability of different materials, the corresponding operating temperature range is also different. It is worth noting that the maximum operating temperature of neodymium is significantly lower than its Curie temperature. Within the operating temperature range, as the temperature increases, the magnetic force of the magnet will decrease, but after cooling, most of the magnetic properties can be restored.   There is an obvious positive correlation between Curie temperature and operating temperature: Generally speaking, the higher the Curie temperature of a magnetic material, the higher its corresponding upper limit of operating temperature, and the better its temperature stability. Taking sintered NdFeB material as an example, by adding elements such as cobalt, terbium, and dysprosium to the raw materials, its Curie temperature can be effectively increased, which is why high coercivity products (such as H, SH, etc. series) generally contain dysprosium.   Even for the same type of magnet, different grades of products have different temperature resistance due to differences in composition and microstructure. Taking NdFeB magnets as an example, the maximum operating temperature range of different grades of products is roughly between 80℃ and 230℃.   Working temperature of sintered NdFeB permanent magnets Coercivity Level Max Working Temperature N Normal 80 ℃ M Medium 100 ℃ H High 120 ℃ SH Super High 150 ℃ UH Ultra High 180 ℃ EH Extremely High 200 ℃ AH Aggressively High 230 ℃   Factors affecting the actual working temperature of NdFeB magnet   Shape and size of neodymium magnets: The aspect ratio of the magnet (i.e., the permeability coefficient Pc) has a significant impact on its actual maximum operating temperature. Not all H-series NdFeB magnets can work normally at 120°C without demagnetization. Some magnets of special sizes may even demagnetize at room temperature. Therefore, for such magnets, it is often necessary to increase their actual maximum operating temperature by increasing the coercivity level.   The degree of closure of the magnetic circuit: The degree of closure of the magnetic circuit is also an important factor affecting the actual maximum operating temperature of the magnet. For the same magnet, the higher the degree of closure of its working magnetic circuit, the higher the maximum operating temperature it can withstand, and the more stable the magnet performance. It can be seen that the maximum operating temperature of the magnet is not a fixed value, but will change dynamically with the change of the degree of closure of the magnetic circuit.