Effect of Heat Treatment on Microstructure and Thermal Stability of Nd-Fe-B Sintered Magnets

The effect of heat treatment on the microstructure and thermal stability of sintered Nd-Fe-B magnets was investigated. The results show that the microstructure of the magnets was greatly affected by heat treatment. The intrinsic coercivity (H(cj)) was increased and the temperature coefficient of coercivity (beta) was decreased by heat treatment. As the annealing temperature changes from 500 degrees C to 770 degrees C, first increases and reaches a maximum, then starts to decrease, but beta emains unchanged from 500 degrees C to 680 degrees C and increases rapidly when annealed over 680 degrees C. A magnet with H(cj) = 30.55 kOe, beta(from 20 degrees C to 200 degrees C) = -0.4079%degrees C was obtained after annealed at 620 degrees C for 2 h. The relationship between the annealing temperature and magnetic properties was studied.