How are sintered NdFeB magnets produced?

2022-11-08

Sintered Nd-Fe-B permanent magnets are produced by powder metallurgy. There are three major process links in raw material production - blank processing - surface treatment, and each link is subdivided into several small links.

Sintered NdFeB permanent Magnetic Material is a permanent magnetic material based on the intermetallic compound Nd2Fe14B. Its main components are Nd, Fe and B. In order to obtain different properties, neodymium in the material can be partially replaced by dysprosium (Dy), praseodymium (Pr) and other rare earth metals, and iron can be partially replaced by cobalt (Co), aluminum (A) and other metals. Nd2Fe14B compound, with tetragonal crystal structure, high saturation magnetization and uniaxial anisotropy field, is the main source of permanent magnetic properties of Nd-Fe-B permanent magnetic materials.
The raw material ratio of sintered NdFeB is very important, which relates to whether the product quality and magnetic properties can meet customer requirements. Different ratios affect the brand of permanent magnetic materials.

The relative density of sintered NdFeB powder compacts is relatively high, the contact between particles is mechanical contact, and the bonding strength is low. In order to further improve the density, improve the contact property between powder particles, increase the strength, and make the magnet have the microstructure characteristics of high permanent magnetic properties, it is necessary to heat the compacts to the temperature below the basic phase melting point of the powder, and conduct heat treatment for a period of time. This process is called sintering.

After the sintered magnet is quenched at high temperature, the grain boundary phase distribution is uneven and the grain boundary is not clear. Therefore, it is necessary to conduct tempering treatment at a certain temperature to optimize the structure and obtain the best magnetic properties. Tempering refers to cooling the sintered magnetic powder blank to a certain temperature and then heating again to raise the temperature. The tempering temperature shall be determined by test or thermal difference analysis.

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