Effects of solution temperature and Cu content on the properties and microstructure of 2:17-type SmCo magnets

The effects of solution temperature and Cu content on the properties and microstructure of Sm (Co_balFe_0.21Cu_xZr_0.03)_7.6 (x = 0.06, 0.08, 0.10) permanent magnets were investigated systematically. The results showed that TbCu₇ single-phase was obtained after solution treatment at optimum temperature. The best magnetic properties of Br = 1.010 T and (BH)_max = 190.2 kJ/m³ were obtained for Sm (Co_balFe_0.21Cu_0.08Zr_0.03)_7.6 by a proper solution treatment at 1478 K. At a lower solution temperature, the Co-rich FeCoZr phase was monitored, and a “step” was observed in the demagnetization curves of aged samples. At a higher solution temperature, composition segregation of the matrix gradually occurs, and a Zr-rich SmCoZr phase was found. However, at a slightly higher solution temperature with superabundant Cu, the precipitated phase remained FeCoZr phase, resulting in a worse remanence. All the above changes were related to the cellular structures.