The phase and microstructure analysis of Alnico magnets with high coercivity

• We developed Alnico9h magnets (Br about 8.5 kGs, Hc about 2020 Oe, (BH)m about 9.5 MGOe).
• Elucidate the structure–property relationships of Alnico.
• The higher intrinsic coercivity could be due to the more clear boundary between two phases.
• The inhomogeneous distribution of Cu atom in α2 would be beneficial for coercivity.

Alnico magnets with high coercivity and high magnetic energy (Hc about 2020 Oe, (BH)m about 9.5 MGOe) are obtained by adjusting chemical compositions and optimizing microstructure. The phase and microstructure of Alnico magnets with high (Alnico9h) and low coercivity (Alnico9) are analyzed contrastively. The shape and distribution of FeCo-rich phase (α1) which are needle-like arrangement in Alnico9h are nonuniform, the orientation degree and the volume fraction of α1 phase are less than that of Alnico9. Energy-dispersive X-ray spectroscopy (EDS) research shows that Fe and Co atoms of α1 phase have a homogeneous distribution in Alnico9h magnet in which the boundaries between α1 and AlNi-rich phases (α2) are clearer than those in Alnico9 magnet. Furthermore, the degree for chemical segregation between α1 and α2 phases in Alnico9h is much better than that in Alnico9 magnet.