Microstructure characteristics and optimization of 2:17-type Sm-Co sintered magnets with different iron content

Abstract

In this work, the dependence of microstructure and magnetic properties on the iron content for Sm(CobalFexCu0.073Zr0.024)7.6 (x = 0.226, 0.233 and 0.24) magnets has been systematically studied. The magnet with x of 0.226 (relatively low Fe content) shows a homogeneous microstructure and optimal magnetic properties after it has undergone a solid solution treatment for only 2 h at 1443 K. However, under the same solid solution treatment, a largely uneven composition distribution is observed in magnets with an increased Fe content (x = 0.24). As a result, the peak and gradient of Cu concentration in the cellular boundaries are lower, giving rise to poor magnetic properties. It is impressive that there Cu precipitates are found in the as-solutionized magnet though the cellular structure has not yet occurred. Our results show that a prolonged solid solution treatment (ts) is necessary to improve the microstructure and magnetic properties of the magnets with higher Fe content. Moreover, the optimal ts can be shortened by increasing the solid solution temperature (Ts). However, when the Ts is too high, the composition is not uniform but segregated, and the magnet shows poor magnetic properties as well. Furthermore, it is also found that the homogeneous microstructure and optimal magnetic properties are deteriorated when the magnets undergo a solution treatment at much higher Ts. However, it can be recovered if the magnet is further solution treated at the proper conditions. Our results suggest that the transformation of microstructure and magnetic properties can be controlled reversibly by adjusting the solution treated conditions.