Improving the magnetic properties of FeSiBC soft magnetic composites by flake powder orientation and mixing with FeSiBCCr fine powder

In this study, toroidal soft magnetic composites (SMCs) with the same specifications, positively engraved (FeSiBC-F) and side-engraved (FeSiBC-S) were prepared by pressing FeSiBC amorphous flake powder into a block, and then engraving from the front part and the side part, respectively. In addition, different mass fractions of FeSiBCCr amorphous spherical fine powder were mixed in the FeSiBC flake powder. Therefore, the effects of flake powder orientation and mixed FeSiBCCr fine powder on the magnetic properties of the compound SMCs were investigated deeply. The results show that FeSiBC-F has higher permeability and lower loss than FeSiBC-S as well as FeSiBCCr SMCs. This is because the powder's long axis in FeSiBC-F is parallel to the diameter direction of the SMCs, originating from the demagnetization effect induced by the shape anisotropy of the flake powder. Calculations of the loss separation of the compound SMCs mixed with FeSiBCCr fine powder show that the eddy current energy loss is only 1/120-1/200 of the total energy loss that can be neglected, which is due to the high resistivity and integrity of the insulating layer. While the hysteresis energy loss and excess energy loss are affected by the density of compound SMCs and the volume fraction of non-magnetic pores, which dominate the total energy loss and tend to decrease initially, then increase as the mass fraction of FeSiBCCr amorphous spherical fine powder increases. Compared with pure FeSiBC SMCs, compound SMCs with the optimal microstructure can be obtained by mixing 15 wt% of FeSiBCCr fine powder, resulting in an all-around improvement in comprehensive soft magnetic properties. Its permeability increased from 66.69 to 67.34, and the DC bias performance at 100 Oe improved by 0.77%. The total loss decreased from 165.48 mW/cm3 to 153.39 mW/cm3 at 100 kHz, 500 Gs. It is shown that mixing appropriate amount of amorphous spherical fine powder in FeSiBC amorphous flake powder to fill the non-magnetic pores is an effective way to optimize the microstructure of amorphous SMCs, and to fully utilize the high-frequency soft magnetic properties of amorphous SMCs.