| In order to study a relation between microstructures and magnetic properties in Alnico 5, Fe-24Co-14Ni-8Al-3Cu alloy was prepared by induction melting, and then optimum heat treatment procedures and microstructures of this alloy were investigated systematically. In Alnico 5, the cooling rate(c) in a magnetic field from 900℃ to 600℃ and the optimum aging time(t) at 600℃ have a relation of log(t)=0.417 log(c) + 0.884. However, the final magnetic properties are highly dependent on the cooling rate. Spinodally decomposed structures of this alloy show that the faster the cooling rate, the smaller the size of the FeCo-rich precipitates and the larger the aspect ratio. Length of the long axis of the FeCo-rich precipitates at a given cooling rate is not uniform due to the interconnection of sub sequent precipitates by magnetic field effect, and this tendency seems to be stronger when the cooling rate is slower. But the length of the short axis of the precipitates is almost same at a given cooling rate. The length of the short axis (ℓ) and cooling rate (c) in magnetic field have a relation of log (ℓ)=2.385-0.317 log(c) Optimum solution treatment temperature of the low temperature solution treatment method is 860℃. It is concluded that the low temperature solution treatment method is more desirable than the high temperature solution treatment method in improving the hard magnetic properties |
|
