The service life of NdFeB—the long-term stability of permanent magnets

If the magnet is working or left for a long time, the surrounding environment (such as temperature, humidity, corrosive liquids, etc.) may cause the physical and chemical properties of the magnet to change. After the permanent magnet is magnetized, most areas are magnetized to a specific direction, but there are still some small magnetic domains whose magnetization directions are chaotic (called reverse magnetization nuclei). Under the action of various environmental factors, the original reverse magnetization nuclei As it grows, new countermagnetized nuclei will be produced, which causes the magnetic properties of the permanent magnet to decay. This change is generally a slow and irrecoverable change from the surface to the inside, which directly affects the main performance parameters of the magnet, such as residual magnetism, coercive force or maximum magnetic energy product, and even leads to complete failure of the magnet. This loss of magnetic performance is irrecoverable, and even if the magnet is re-magnetized, it cannot return to the level before it was left for a long time. 

In recent years, with the wide application of NdFeB permanent magnet materials in aerospace, electric vehicles, high-power wind turbines and other fields that require long service life, application designers are concerned about the time stability of NdFeB permanent magnets. Pay more and more attention to it.

Usually, large magnetic flux loss comes from oxidation or corrosion of the magnet surface, which is an irrecoverable loss. Among various types of rare earth permanent magnet materials, this loss of sintered NdFeB is the most serious. However, after composition optimization and Surface protection treatment, oxidation resistance and corrosion resistance of sintered NdFeB magnets have been greatly improved. Therefore, if the magnet surface is well protected, the service life of sintered NdFeB with sufficiently high HcJ can exceed 30 to 50 years. (This is under the condition that the operating temperature is not exceeded~)