Microstructure and magnetic properties of alnico permanent magnetic alloys with Zr-B additives

Alnico alloys are prepared with nominal composition of 31.4-xFe-7.0Al-36.0Co-4.0Cu-1.0Nb-14.0Ni-6.0 Ti-0.6Zr-xB (x = 0.02, 0.04, 0.06, 0.08, in wt%) by arc melting and casting techniques and subsequent heat treatment. The alloys are characterized by X-ray diffraction method, optical microscope, scanning electron microscope and pulse field magnetometer by plotting magnetic hysteresis demagnetization curve. The results of HRSEM show at least two new phases at alpha-grain boundaries and triple junctions. These phases, when retained at low concentration, help in enhancing magnetic properties of alnico alloys by purifying spinodal phases and reducing the adverse effects of impurity elements. Two different heat treatment cycles are employed. In the first phase, the alloys are processed by using heat treatment cycles without magnetic field; and H-c of 1.35 kOe, B-r of 4.87 kGs and (BH)(max) of 1.96 MGOe are obtained by furnace cooling below T-C and subsequent tempering at 680 degrees C and 550 degrees C. In the second phase, the alloy with best magnetic properties is treated thermo-magnetically; and H-c of 1.68 kOe, B-r of 7.1 kG and (BH)(max) of 4.45 MGOe are obtained. (C) 2017 Elsevier B.V. All rights reserved.