With the development of society, the application of magnets has become wider and wider, from high-tech products to the simplest packaging magnets. Permanent magnet materials include ferrite permanent magnets, rare earth permanent magnets, aluminum nickel cobalt, iron chromium cobalt, aluminum iron and other materials. Among them, the most commonly used and most used are ferrite permanent magnets and neodymium iron boron rare earth permanent magnets.
The rare earth permanent magnet materials are mainly rare earth cobalt permanent magnet materials and neodymium iron boron permanent magnet materials. The rare earth cobalt permanent magnet material is an intermetallic compound formed by the rare earth elements cerium, praseodymium, lanthanum, neodymium, etc. and cobalt. Its magnetic energy product can reach 150 times that of carbon steel and 3 to 5 times that of alnico permanent magnet materials. 8 to 10 times the body, this permanent magnetic material has a low temperature coefficient, stable magnetic properties, and high coercivity. Mainly used in the magnetic system of low-speed torque motors, starting motors, sensors, magnetic thrust bearings and other products.
NdFeB permanent magnet material is the third-generation rare earth permanent magnet material. Its remanence, coercivity and maximum magnetic energy product are higher than those of rare earth cobalt permanent magnet materials. It is not fragile, has good mechanical properties, and has low alloy density, which is beneficial to The light, thin, small and ultra-miniaturized magnetic components are currently the most used materials for permanent magnet motors . But its high magnetic temperature coefficient limits its application.
Overview of permanent magnet materials
Permanent magnetic materials are also called "hard magnetic materials". A material that maintains a constant magnetic property once it is magnetized. It has wide hysteresis loop, high coercivity and high remanence. In practice, the permanent magnet material works in the second quadrant demagnetization part of the magnetic hysteresis loop after deep magnetic saturation and magnetization. Commonly used permanent magnet materials are divided into Al-Ni-Co-based permanent magnet alloys, Fe-Cr-Co-based permanent magnet alloys, permanent ferrites, rare earth permanent magnet materials and composite permanent magnet materials, which are briefly described as follows:
●Al-Ni-Co-based permanent magnet alloy. With iron, nickel, and aluminum as the main components, it also contains copper, cobalt, titanium and other elements. With high remanence and low temperature coefficient, magnetic stability. There are two types of casting alloys and powder sintered alloys. This material was widely used in the 1930s to 1960s, and is now used in the instrument industry to manufacture magnetoelectric meters, flow meters, micro motors, relays, etc.
●FeCrCo permanent magnet alloy. With iron, chromium, and cobalt as the main components, it also contains molybdenum and a small amount of titanium and silicon. Its processing performance is good, it can undergo cold thermoplastic deformation, its magnetic properties are similar to that of AlNiCo permanent magnet alloys, and its magnetic properties can be improved through plastic deformation and heat treatment. It is used to manufacture all kinds of small magnetic components with small cross-section and complex shape.
●Permanent ferrite. There are mainly barium ferrite and strontium ferrite, which have high resistivity and high coercivity, and can be effectively used in large gap magnetic circuits, and are especially suitable for permanent magnets in small generators and motors. Permanent magnet ferrite does not contain precious metals such as nickel, cobalt, etc. It has a rich source of raw materials, simple process and low cost, and can replace AlNiCo permanent magnets to manufacture magnetic separators, magnetic thrust bearings, speakers, microwave devices, etc. However, its maximum magnetic energy product is low, temperature stability is poor, and the texture is brittle, fragile, and not resistant to shock and vibration. It is not suitable for measuring instruments and magnetic devices with precision requirements.
● Rare earth materials. They are mainly rare earth cobalt permanent magnet materials and neodymium iron boron permanent magnet materials. The properties of this material have been described in relative detail in the previous part of this article, and will not be repeated here; this material is currently one of the main production materials for permanent magnet motors .
●Composite materials. It is composed of permanent magnetic material powder and plastic material as a binder. Because it contains a certain proportion of binder, its magnetic properties are significantly lower than the corresponding magnetic material without binder. Except for metal composite permanent magnetic materials, other composite permanent magnetic materials are limited by the heat resistance of the binder, so the service temperature is relatively low, generally not exceeding 150°C. However, the composite permanent magnet material has high dimensional accuracy, good mechanical properties, and good uniformity of the performance of each part of the magnet, and it is easy to carry out the radial orientation and multi-pole magnetization of the magnet. Mainly used in the manufacture of instruments and meters, communication equipment, rotating machinery, magnetic therapy equipment and sporting goods, etc.
