Transactions of Nonferrous Metals Society of China
JOURNAL OF RAILWAY SCIENCE AND ENGINEERING
|Vol. 17 No. 3 June 2007|
（School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China）
Abstract: The quenching, fracture and aging treatment of radially oriented Sm2Co17 ring magnets were investigated. The results indicate that the ring magnets have obvious anisotropy of thermal expansion, which easily leads to the splits of the magnets during quenching. The fracture is brittle cleavage fracture. The difference (Δa) of the expansion coefficient reaches the maximum value at 800−850 ℃. So, various quenching processes at different steps are adopted in order to reduce the splits. When the magnets are aged, 1׃5 phase precipitates from the 2׃17 matrix phase and forms a cellular microstructure with 2׃17 phase. BHmax and JHc reach the maximum value 226 kJ/m3 and 2 170 kA/m after being aged at 850 ℃ for 4 h and 8 h, respectively. The aging treatment at 850 ℃ has little influence on remanence(Br), which can always keep a high value (≥1.0 T). Through appropriate heat treatment, the ring magnets have uniform cellular microstructure and excellent magnetic properties: Br≥1.0T, JHc≥2 100 kA/m, BHmax≥220 kJ/m3.
Key words: Sm2Co17 permanent magnets; radially oriented ring magnets; heat treatment; fracture; magnetic properties