The effects of post-processing on longitudinal magnetostriction and core losses of high saturation flux density FeSiBC amorphous alloy ribbons and cores

Abstract

Fe-based amorphous soft magnetic materials play an attractive role in energy saving and emission reduction due to low core losses. One of the problems is the acoustic noise resulting from magnetostriction during AC magnetization process. In this work, amorphous ribbons with a nominal composition of Fe81.5Si4B14C0.5 (at. %) were produced by planar flow casting and subjected to various postprocessing treatments. The influences of annealing conditions on the longitudinal magnetostriction, acoustic noise and core losses of the ribbons measured at low-field were studied. The effects of bending stress and epoxy impregnation and curing on medium frequency core losses of the alloy cores with different shapes were also investigated. It is shown that larger longitudinal magnetostriction of amorphous ribbons leads to higher acoustic noise emission from amorphous cores. Although the longitudinal magnetostriction was found to be reduced by applying a longitudinal magnetic field during annealing, the core loss was increased. The minimum longitudinal magnetostriction value at 1000 A/m is 7 ppm for ribbon annealed at 350 °C for 90 min. under an applied longitudinal magnetic field, while the lowest core losses at 1.4 T and 50 Hz is 0.213 W/kg for toroidal core annealed at 350 °C for 90 min. under an applied transverse magnetic field. The coupling between longitudinal magnetostriction and bending stress of amorphous ribbon results in an increase in core losses. Furthermore, extra stress was introduced after epoxy impregnation and curing, which also results in an increase in core losses. Thus, low longitudinal magnetostriction is important for stress insensitivity and soft magnetic properties.