Effects of Zr alloying on the microstructure and magnetic properties of Alnico permanent magnets

Alnico-8 permanent magnets were produced through casting and subsequent thermal treatment process. Magnetic alloy of nominal composition 32.5 Fe-7.5 Al-1.0 Nb-35.0 Co-4.0 Cu-14.0 Ni-6.0 Ti were prepared by arc melting and casting technique. The Zr was added to 32.5 Fe-7.5 Al-1.0 Nb-35.0 Co-4.0 Cu-14.0 Ni-6.0 Ti alloy ranging from 0.3 to 0.9 wt%. The magnets were developed by employing two different heat treatment cycles known as conventional treatment and thermo-magnetic annealing treatment. The samples were characterized by X-ray diffraction method, Scanning electron microscope and magnetometer by plotting magnetic hysteresis demagnetization curves. The results indicate that magnetic properties are strongly depended upon alloy chemistry and process. The 0.6 wt% Zr added alloys yielded the best magnetic properties among the studied alloys. The magnetic properties obtained through conventional heat treatment are H-c = 1.35 kOe, B-r = 5.2 kG and (BH)(max) = 2 MGOe. These magnetic properties were enhanced to H-c = 1.64 kOe, B-r = 6.3 kG and (BH)(max) = 3.7 MGOe by thermo-magnetic annealing treatment. (C) 2017 Elsevier B.V. All rights reserved.