Identification of optimal solid solution temperature for Sm 2 Co 17 -type permanent magnets with different Fe contents

It is confirmed that the solid solution temperature range to obtain optimal magnetic properties is different for the magnets with different Fe contents, and the correlation between magnetic properties and microstructures influenced by solid solution temperature (Ts) has been systematically studied. The optimal solid solution temperature range is 1413–1463 K for the Sm(CobalFe0.213 Cu0.073Zr0.024)7.6 magnet, which is higher than that of the Sm(CobalFe0.262Cu0.073Zr0.024)7.6 magnet (1403–1453 K), and the optimal Ts range is about 50 K for both of the magnets. The solid solution temperature range shifting toward relatively high temperature is due to the increase in a phase transition temperature. The magnet solution-treated at proper temperature exhibits 1:7H single phase, and intact cell structure and high Cu concentration (23.12 at%) in the cell boundary are found after aging process, which makes the magnet shows high intrinsic coercivity (Hcj) and magnetic field at knee-point (Hknee). At a lower solid solution temperature, the 2:17H, 1:5H and Zr-rich precipitation phases appear, which affects the cell structure, density of lamellar phase and Cu concentration in the cell boundary, leading to the reduced magnetic properties. However, at a higher solid solution temperature, there exist obviously light gray and dark regions with different Sm, Cu and Fe contents in scanning electron microscopy observation, and the magnet shows low pinning field in the two regions and incomplete cell structure, resulting in an inferior Hcj and Hknee.