The influence of final aging temperature on thermal stability of microstructure and magnetic properties in Sm(Co,Fe,Cu,Zr)z high temperature magnets

The change of microstructure and magnetic properties after heated to high temperature remains a critical concern for the application of SmCo magnets. In this work, the influence of final aging temperature on thermal stability of microstructure and magnetic properties in Sm(Co0.777Fe0.1Cu0.09Zr0.033)7.61 high temperature magnets is studied. Meanwhile, the main structure determining the magnetic loss and underlying mechanism are discussed. The results show that the flux loss mainly stems from the reversed domain structure at grain boundaries, which are defects with incomplete cellular nanostructures. Thus, grain size is the key factor determining the flux loss. When the final aging temperature increases from 400 to 600 °C, the grain size decreases monotonically, leading to higher flux loss. On the other hand, the microstructure and magnetic properties tend to reach the equilibrium state at the operating temperature. Therefore, the thermal stability of microstructure and magnetic properties can be enhanced by reducing the temperature difference between final aging temperature and operating temperature. This work offers in-depth insights into the fundamental understanding of magnetic loss and provides methods to reduce magnetic loss in 2:17-type SmCo magnets. The flux loss can be reduced by increasing the grain size, while irredeemable magnetic properties loss can be reduced by increasing the thermal stability of microstructure.