Preparation process of sintered NdFeB magnet

Sintered NdFeB refers to a type of permanent magnet made from a combination of neodymium, iron, and boron powders, which are mixed together and then sintered (heated until they fuse together) to form a solid magnet. Sintered NdFeB magnets are known for their extremely high magnetic strength, which makes them useful in a wide range of applications, including computer hard drives, wind turbines, electric motors, and speakers.

Next is the introduction about the preparation process of sintered NdFeB magnets:

Raw material pretreatment.

Crushing, mixing, and pre-synthesis of raw materials such as neodymium, iron, and boron. During the crushing process, an air jet mill is usually used to crush the raw materials to an average particle size within the range of 3-5 μm. In the mixing process, mechanical or liquid-phase mixing can be used to evenly distribute the elements. The pre-synthesis process is mainly to improve the magnetic properties and reduce oxidation during subsequent sintering.

Pressing and forming.

The pre-treated raw material powder is pressed into the desired shape of the green compact using isostatic or uniaxial pressing methods. Organic binders and lubricants can be added to improve the forming performance.

Debinding and sintering.

The green compact is debinded to remove organic binders and lubricants. Debinding methods include thermal debinding, chemical debinding, and vacuum debinding. The sintering process is usually carried out in a vacuum or protective atmosphere sintering furnace, with a sintering temperature of generally 1080-1120℃ and a sintering time of 1-3 hours.

Magnetic field alignment and annealing.

The sintered magnet is aligned in a magnetic field to improve its magnetic properties. During the alignment process, the magnet is heated to about 850℃ in a high magnetic field (about 30-50 kOe), and then cooled to room temperature in the magnetic field. Annealing is mainly to eliminate stress and defects generated during the sintering process and is usually carried out in a vacuum or protective atmosphere furnace, with an annealing temperature of 450-550℃ and an annealing time of 2-10 hours.

Machining, coating, and magnetization.

The magnet is machined by cutting and grinding to achieve the desired size and shape. Coating is usually performed using methods such as nickel plating, zinc plating, or gold plating to improve the magnet's corrosion resistance. Finally, the magnet is magnetized in a high magnetic field to achieve the desired magnetic pole distribution.

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