Effect of annealing temperature on coercivity of Nd–Fe–B magnets with TbFeAl doping by process of hot-pressing**Project supported by the Major Project of “Science and Technology Innovation 2025” in Ningbo City, China (Grant Nos. 2018B10086 and 2018B10017).

Abstract

The Nd–Fe–B magnets are pre-sintered and then processed with hot-pressing, and the resulting magnets are 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 °C, the coercivity of the magnet is only 17.6 kOe (1 Oe = 79.5775 A⋅m–1), but when the annealing temperature rises up to 1060 °C, the coercivity of the magnet reaches 23.53 kOe, which is remarkably increased by 33.7%. The microstructure analysis indicates that the grain surface of the HPP magnet becomes smoother as the annealed temperature increases. The microstructure factor α is changed according to the intrinsic coercivity model formula. The α of the magnet at 900 °C is only 0.578, but it is 0.825 at 1060 °C. Microstructural optimization is due mainly to the increase of coercivity of the HPP magnet.