Effect of Annealing on the Magnetism of the Sintered NdFeB Magnet

摘要

This paper deals with the effect of annealing on the magnetism of the sintered NdFeB magnet with a composition of Nd_(30)B_(5.1)Dy_(1.2)Al_(0.6)Nb_(0.7)Fe_(62.4). 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 Nd_2Fe_(14)B main phase will decrease it. When the sintered NdFeB magnet was annealed at 3Pa and 492℃ for an hour the coercive force would raise from 915.6kA/m to 1164.8kA/m, and the (BH)_(max) from 277.7kJ/m to 349.5kJ/m. However, annealing at a non-optimized temperature at 542℃, microstructure changes in some main phase will leading the decrease of properties.