Fabrication and Magnetic Properties of FeSiB-based Soft Magnetic Composites

FeSiB soft magnetic composites (SMCs) were prepared via powder metallurgy with FeSiB ribbons as starting material. Influences of passivator solvent, content of the passivator as well as annealing temperature on the morphology and properties of the samples were investigated. Alcohol was used to dissolve phosphoric acid as the surface passivator and its effect was compared with that of water and acetone. Results show that the magnetic powders are prone to oxidation with water, while acetone hinders the complete surface passivation as a result of limited reaction time caused by low boiling point and strong volatility of the acetone. A uniform insulating coating can be achieved using alcohol as the passivator solvent and it decreases core loss of the composites. With the content of orthophosphoric acid varying between 0.2 similar to 0.8 wt% in alcohol, lowest core loss (187 mW/cm(3) measured at 50 kHz, 50 mT) can be obtained with 0.6 wt% of orthophosphoric acid. Stress relaxation is insufficient when the annealing temperature is below 400 degrees C for the SMCs, resulting in low permeability and high core loss, while precipitation and crystallization of the alpha-Fe phase occur with annealing temperatures higher than 425 degrees C. Optimum properties of the FeSiB SMCs can be achieved by annealing at 400 similar to C for 1 h.