With the development of society, magnets are used more and more widely, from high-tech products to the simplest packaging magnets. Permanent magnet materials include ferrite permanent magnets, rare earth permanent magnets, alnico, iron chromium cobalt, aluminum iron and other materials. Among them, the most commonly used and consumed are ferrite permanent magnets and neodymium iron boron rare earth permanent magnets.
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 that of the body. This permanent magnet material has a low temperature coefficient, stable magnetism and high coercive force. Mainly used in magnetic systems of low-speed torque motors, starter motors, sensors, magnetic thrust bearings and other products.
NdFeB permanent magnet material is the third generation of rare earth permanent magnet material. Its remanence, coercivity and maximum magnetic energy product are higher than those of rare earth cobalt permanent magnet material. It is not fragile, has good mechanical properties, and has low alloy density, which is beneficial to Light, thin, small and ultra-miniaturized magnetic components are currently the permanent magnet motor Use the widest range of materials. However, its magnetic temperature coefficient is high, which limits its application.
Overview of permanent magnet materials
Permanent magnetic materials are also called "hard magnetic materials". A material that maintains constant magnetism once magnetized. It has a wide hysteresis loop, high coercivity and high remanence. In practice, permanent magnet materials work in deep magnetic saturation and the second quadrant demagnetization part of the hysteresis loop after magnetization. Commonly used permanent magnet materials are divided into Alnico permanent magnet alloys, iron-chromium-cobalt permanent magnet alloys, permanent magnet ferrites, rare earth permanent magnet materials and composite permanent magnet materials. Now they are briefly described as follows:
●Alnico permanent magnet alloy. It is mainly composed of iron, nickel, and aluminum elements, and also contains elements such as copper, cobalt, and titanium. It has high remanence and low temperature coefficient, and is magnetically stable. There are two types: cast alloy and powder sintered alloy. This material was widely used from the 1930s to the 1960s, and is now mostly used in the instrument industry to manufacture magnetoelectric instruments, flow meters, micro motors, relays, etc.
●Iron-chromium-cobalt permanent magnet alloy. It is mainly composed of iron, chromium and cobalt elements, and also contains molybdenum and a small amount of titanium and silicon elements. It has good processing performance and can undergo cold and hot plastic deformation. Its magnetic properties are similar to Alnico permanent magnet alloy, and its magnetic properties can be improved through plastic deformation and heat treatment. Used to manufacture various small magnet components with small cross-sections and complex shapes.
●Permanent ferrite. There are mainly barium ferrite and strontium ferrite, which have high resistivity and large coercivity. They can be effectively used in large-gap magnetic circuits and are especially suitable for permanent magnets in small generators and motors. Permanent ferrite does not contain precious metals such as nickel and cobalt. It has rich sources of raw materials, simple technology and low cost. It can replace AlNiCo permanent magnets in the manufacture of magnetic separators, magnetic thrust bearings, speakers, microwave devices, etc. However, its maximum magnetic energy product is low, its temperature stability is poor, its texture is brittle and fragile, and it is not resistant to shock and vibration. It is not suitable for use as measuring instruments and magnetic devices with precision requirements.
●Rare earth materials. Mainly rare earth cobalt permanent magnet materials and neodymium iron boron permanent magnet materials. The characteristics of this material have been described in relatively detail in the previous part of this article and will not be repeated here; this material is the current permanent magnet material. Motor One of the main production materials.
●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 materials without binder. Except for metal composite permanent magnet materials, other composite permanent magnet materials are limited by the heat resistance of the binder and have a lower operating temperature, generally not exceeding 150°C. However, the composite permanent magnet material has high dimensional accuracy, good mechanical properties, good performance uniformity of each part of the magnet, and is easy to carry out radial orientation of the magnet and multi-pole magnetization. Mainly used in manufacturing instruments, communication equipment, rotating machinery, magnetic therapy equipment and sporting goods.
