Permanent magnet alloys are an important component of modern electromechanical products and systems. Permanent magnet alloys are composed of iron, cobalt, aluminum, nickel and other elements, and are divided into sintered and bonded types. Permanent magnet alloys have high magnetic properties and are widely used in automotive motors, micro motors, servo motors, scanning mirrors, magnetic sensors, instrumentation, magnetic lifts, loudspeakers and other products and fields.
The microstructure of permanent magnet alloys has a great influence on the magnetic properties. Taking sintered NdFeB magnets as an example, its main crystal form is an orthorhombic form with the Nd2 Fe14 B structure, and the grain boundary is composed of K2 Nd3 Fe17 alloy. The NdFeB microstructure is conservative, usually in the form of needle structure, block structure and small lamellar structure. The coercivity is proportional to the length of the needle particles; the average magnetic flux density is related to the maximum thickness of the needle particles, that is, the crystal size; the remanence ratio is related to the complexity of the microstructure.
The production process of permanent magnets affects the performance and processing quality of the products. The processing of sintered NdFeB magnets includes powder preparation, processing, sintering and performance testing. Before sintering, the powder should be screened, homogenized and the shape should be optimized to improve the sintering performance. In the sintering process, temperature, dwell time, atmosphere and pressure should be controlled, and a balanced system of sintering and tempering should be used to guarantee the properties of the products. After sintering, the size and shape of the product can be finished by secondary processing.
The application of low-temperature sintering NdFeB magnets has gradually become the development direction of permanent magnet alloys. Low temperature forming technology includes self-initiated sintering, spark sintering, microwave sintering and electroplating forming. Low temperature forming not only has the advantages of low cost, high efficiency, low energy consumption and no pollution, but also can improve the utilization rate of raw materials, refine the microstructure, reduce the grain size, enhance the saturation magnetization and improve the coercivity.
At present, the research on professional fields such as the sintering and performance of permanent magnets, surface processing and low temperature forming, various shapes and improved performance of permanent magnets is still in-depth. The research and development of permanent magnet alloys should also focus on the optimization of microstructure and alloy composition, refinement of powder and reduction of sintering cost. In addition, the research and development of magnets with high magnetic energy product, low loss and light weight should be strengthened, and the application range of permanent magnets in electronic technology should be further expanded.
