Effect of annealing treatment on the magnetic properties with wide temperature range of Co-doped FeSi soft magnetic composites

Fe-Si-Co soft magnetic composites (SMCs) coated with silicone resin were successfully prepared in this work. The influences of annealing treatment on the temperature/frequency-dependent behaviors of magnetic properties for SMCs were studied by microstructure analysis and loss separation. Results show that the core loss of Fe-6.5Si-1.0Co SMCs gradually decreases with annealing temperatures rising from 500 degrees C to 700 degrees C when measured at 50 kHz, while the core loss of Fe-6.5Si-3.0Co SMCs first decreases then increases. Meanwhile, the effective permeability Fe-6.5Si-1.0Co and Fe-6.5Si-3.0Co SMCs are significantly improved. Simultaneous optimization for core loss and effective permeability benefits from the residual stress relief and defect elimination induced by annealing. Fe-6.5Si-1.0Co SMCs annealed at 700 degrees C shows excellent comprehensive performances with core loss of 766.7 mW/cm3 and effective permeability of 112.3 measured at 0.1 T / 50 kHz. While annealing at excessive temperature causes the phase transition and change in resistance of silicone-resin coatings, leading to the rapid deterioration of the magnetic performances. As for the temperature characteristics, the Fe-Si-1.0Co SMCs also exhibits good stability for effective permeability and negative correlation for core loss with the measuring temperature ranging from-25 degrees C to 125 degrees C. This work may provide some theoretical support for the wide temperature domain application of the Co-doped FeSi SMCs.