Effect of Annealing on the Magnetism of the Sintered NdFeB Magnet

This paper deals with the effect of annealing on the magnetism of the sintered NdFeB magnet with a composi- tion of Nd3oB5M Alo.6Nbo.7Feft2.4- Microstructural investigations of the grain size and grain boundaries with SEM were carried out. Microstructural investigations showed the presence of some Nd-rich phase in grain boundaries and main phase. The results of magnetic properties analysis shows that this non-magnetic Nd-rich phase, produced in annealing process, can increase or decrease the magnetism of the sintered NdFeB-type permanent magnet. Appropriate amount of Nd-rich phase will strengthen the pinning field and elevated the coercive force of magnet, but too many these non-magnetism phases in Nd2Fei4B main phase will decrease it. When the sintered NdFeB magnet was annealed at 3Pa and 492°C for an hour the coercive force would raise from 915.6kA/m to 1164.8kA/m, and the (BH^ from 277.7kJ/m to 349.5kJ/m. How- ever, annealing at a non-optimized temperature at 542 °C, microstructure changes in some main phase will leading the de- crease of properties.