performance of neodymium magnet

Sintered NdFeB magnets are core functional components and are widely used in instruments and equipment such as motors, electroacoustics, magnetic attraction, and sensors. The magnets are subject to environmental factors such as mechanical force, hot and cold changes, and alternating electromagnetic fields. If the working environment is over the standard, it will seriously affect the function of the equipment and cause huge losses. Therefore, in addition to magnetic performance, we also need to pay attention to the mechanical, thermal, and electrical properties of magnets, which will help us better design and use magnet, and is also of great significance for improving their service stability and reliability.   Mechanical Properties   The mechanical properties of magnets include hardness, compressive strength, bending strength, tensile strength, impact toughness, etc. NdFeB is a typical brittle material. The hardness and compressive strength of magnets are high, but the bending strength, tensile strength, and impact toughness are poor. This makes it easy for magnets to lose corners or even crack during processing, magnetization, and assembly. Magnets are usually fixed in components and equipment by means of slots or adhesives, and shock absorption and buffering protection are also provided.   The fracture surface of sintered NdFeB is a typical intergranular fracture. Its mechanical properties are mainly determined by its complex multiphase structure and are also related to the formula composition, process parameters, and structural defects (voids, large grains, dislocations, etc.). Generally speaking, the lower the total amount of rare earth, the worse the mechanical properties of the material. By adding low-melting-point metals such as Cu and Ga in appropriate amounts, the toughness of neodymium magnet can be enhanced by improving the distribution of grain boundary phases. Adding high-melting-point metals such as Zr, Nb, and Ti can form precipitation phases at the grain boundaries, which can refine the grains and inhibit crack extension, helping to improve strength and toughness; but excessive addition of high-melting-point metals will cause the hardness of the magnetic material to be too high, seriously affecting processing efficiency.   In the actual production process, it is difficult to take both the magnetic properties and mechanical properties of magnetic materials into account. Due to cost and performance requirements, it is often necessary to sacrifice their ease of processing and assembly.   Thermal Properties   The main thermal performance indicators of NdFeB magnets include thermal conductivity, specific heat capacity and thermal expansion coefficient.   The performance of neodymium magnet gradually decreases with the increase of temperature, so the temperature rise of permanent magnet motor becomes a key factor affecting whether the motor can run under load for a long time. Good heat conduction and heat dissipation can avoid overheating and maintain the normal operation of the equipment. Therefore, we hope that the magnetic steel has a higher thermal conductivity and specific heat capacity, so that the heat can be quickly conducted and dissipated, and at the same time, the temperature rise will be lower under the same heat.   Electrical Properties   In the alternating electromagnetic field environment of the permanent magnet motor, the magnetic steel will produce eddy current loss and cause temperature rise. Since the eddy current loss is inversely proportional to the resistivity, increasing the resistivity of the NdFeB permanent magnet will effectively reduce the eddy current loss and temperature rise of the magnet. The ideal high-resistivity magnetic steel structure is to form an isolation layer that can prevent electron transmission by increasing the electrode potential of the rare earth-rich phase, so as to achieve the wrapping and separation of the high-resistance grain boundary relative to the main phase grains, thereby improving the resistivity of the sintered NdFeB magnet. However, neither the doping of inorganic materials nor the layering technology can solve the problem of magnetic performance deterioration. At present, there is still no effective preparation of magnets with both high resistivity and high performance.