Effects of Sintering Time on High-Temperature Magnetic Properties and Microstructure of Sintered Sm(Co0.79Fe0.09Cu0.09Zr0.03)7.68 Magnet

The effects of different sintering time on the microstructure and high-temperature magnetic properties of Sm(Co 0.79 Fe 0.09 Cu 0.90 Zr 0.03 ) 7.68 magnets were studied. As the sintering time increased from 0.5 to 2 h, the room temperature coercivity increased from 30.50 to 32.25 kOe, while the coercivity at 823 K decreased from 5.20 to 4.69 kOe. The microstructure and element distribution were analyzed by scanning electron microscope and transmission electron microscopy. The average grain size increased obviously from 17.86 to $71.21~\mu \text{m}$ , which was beneficial to the increase in coercivity for less grain boundary regions. For solution-treated magnets, 1:7H, 2:17H, Zr 6 Co 23 , and minor 2:17R phases are formed in both magnets. More cubic Zr 6 Co 23 phase and 2:17H phase appeared as the sintering time increased. Cellular structure was observed in both magnets. Furthermore, more Cu content was distributed in the cell boundary phase due to higher density of lamellar phase in magnets with shorter sintering time. The change in Cu distribution altered the coercivity mechanism from repulsive pinning to attractive pinning, which could be the reason for the different high-temperature magnetic properties.