High saturation magnetization and low core loss of FeSiAl soft magnetic composites with Al2O3-Co composite coating designed by interface reactions

The simultaneous improvement of core loss and saturation magnetization remains a challenge for soft magnetic composites (SMCs) used in high-frequency and high-efficiency power electronic devices. In this work, FeSiAl SMCs with Al 2 O 3 -Co composite coating were fabricated via sintering FeSiAl/Co 3 O 4 composite powders, during which interface reactions occurred between FeSiAl and Co 3 O 4 . The influence of Co 3 O 4 coating content on the microstructure and properties of the prepared FeSiAl SMCs was systematically studied. The highly intact Al 2 O 3 coating effectively enhanced the insulation between FeSiAl magnetic particles, thus reducing eddy current loss. Meanwhile, the Co coating effectively weakened the magnetic dilution effect induced by the Al 2 O 3 coating, enabling the FeSiAl SMCs to maintain a high saturation magnetization. With increasing Co 3 O 4 coating content, the thickness of the composite coating increased, leading to an elevated resistivity of FeSiAl SMCs and a continuous decrease in core loss. Furthermore, a moderate increase in Co 3 O 4 content below 7.5 wt% was conducive to improving the saturation magnetization. However, when the coating content exceeded 10.0 wt%, insufficient diffusion of Al atoms toward the reaction interface restricted the interface reaction, resulting in the formation of CoO phase in the composite coating and consequently a decline in saturation magnetization. This work provides a novel strategy for the design and preparation of high-quality inorganic coatings in SMCs.