Intergranular microstructure of Nd-rich phase of sintered NdFeB magnets after thermal extruding

The microstructure of intergranular Nd-rich phase of sintered NdFeB magnets has been studied by means of thermal extruding. After thermal extruding Nd₂Fe₁₇B₇ magnets, Nd-rich phases are not distributed in the intergranular region on the average and a lot of Nd-rich phases aggregate or separate from the magnet. The results show that the microstructure of Nd-rich is consisted of α-Nd phase and Nd₂Fe₁₇ phase, which approaches to eutectic structure of binary Nd-Fe alloy. After adding element Al, Nd₂Fe₁₅Al₂ phases segregate near to the grain boundary of the magnetic Nd₂Fe₁₄B phase, which leads to the improvement of coercivity of magnets.