Effect of annealing temperature on coercivity of Nd–Fe–B magnets with TbFeAl doping by process of hot-pressing

The Nd-Fe-B magnets were first pre-sintered and then processed with hot-pressing, which the resulting magnets were called the hot-pressed pretreated (HPP) magnets. The coercivity of the HPP magnets increases as the annealed temperature increases. When the annealing temperature is 900℃, the coercivity of the magnet is only 17.6 kOe, but when the annealing temperature reaches 1060℃, the coercivity of the magnet reaches 23.53 kOe, which remarkably increased by 33.7%. The microstructure analysis indicates that the grain surface of the HPP magnets becomes smoother as the annealed temperature increases. The microstructure factor α has been changed according to the intrinsic coercivity model formula. The α of the magnet at 900℃ is only 0.578, while the α of the magnet at 1060℃ is 0.825. Microstructural optimization is the main reason for the increase of coercivity of the HPP magnets.