Preparation of Alnico magnet with high magnetization by thermal deformation
Description
To be published on the Materials Letters.
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The Alnico alloy with a nominal composition of 29.5Fe-38Co-14Ni-8Al-7.5Ti-3Cu (equivalent to Alnico 8) was melt-spun at 40 m/s to obtain the Alnico ribbons. The Alnico ribbons were solution-treated at 1250 ℃ for 30 min and water quenched, then, they were annealed at 835 ℃ for 15 min under an additional 5 kOe field and three-step aged at 650 ℃ for 4 h, 600 ℃ for 8 h, and 550 ℃ for 12 h to get the “MHT ribbons”. The compositions of α1 and α2 phases of Alnico 8 are statistically averaged from Ref. [4], they are designed as Fe46.5Co39.7Ni8Al5Ti0.5Cu0.3 of α1 alloy and Fe9Co27.4Ni24.5Al23.5Ti14Cu1.6 of α2 alloy, respectively. The two alloys were arc-melted and melt-spun at 40 m/s to obtain the α1 and α2 ribbons. Then the α1 and α2 ribbons were mixed uniformly in a ratio of 2:1, and the composite ribbons were hot isostatic pressed (HIP) at 920 °C under 135 MPa in a vacuum and hot-rolled (HR) at 1200 °C until the height was reduced by 70% (for short HR magnet). Then the “MHT magnet” was prepared with an HR magnet in the same heat treatment way as the MHT ribbons. The phase composition was analyzed by Rigaku Dmax 2500 Pc X-ray diffractometer. The microstructure was investigated by the Tecnai G2 F20 transmission electron microscope (TEM). The magnetic properties were measured by Lake Shore 7407 vibrating sample magnetometer (VSM).