Influence of the final heat treatment temperature on the magnetic property losses of Sm(Co,Fe,Cu,Zr)_z high temperature magnets

Microstructures of Sm(Co_balFe_0.12Cu_0.07Zr_0.02)₇ high temperature magnets with different final slow cooling aging temperatures were investigated to uncover the underlying mechanism of magnetic property losses after operating at 500 °C. When the final slow cooling aging temperature is 400 °C, lower than the operating temperature, both remanence and coercivity reduce after operating, and cannot be recovered to the initial state. Such losses stem from the secondary diffusion induced microchemistry change in the high temperature environment, which will seriously shorten its service life. While when the final slow cooling aging temperature is 500 °C or higher than the operating temperature, the remanence slightly reduces but the coercivity remains nearly unchanged after operating, and can be recovered to the initial level. Consequently, our comparative investigations suggest that final aging at temperatures equivalent or higher than the operating temperature can not only provide stable and reliable magnetic properties for application, but also extend the service life of the present Sm-Co-based magnets.