Ultra-low core loss FeSiAl soft magnetic composites with in-situ double oxidation layers of outer Fe3O4 layer and inner super-thin Al2O3/SiO2 hybrid layer

How to synchronously reduce eddy current loss and hysteresis loss still remains a challenge for achieving low core loss of soft magnetic composite (SMC). In-situ surface oxide effectively combines the formation of insulating layer and the release of internal stress during the molding process. In this study, FeSiAl SMC has been fabricated by powder metallurgy method with in-situ oxidated FeSiAl powder, in which FeSiAl powder are covered by outer Fe3O4 insulating layer and inter super-thin Al2O3/SiO2 hybrid layer. Fe3O4 layer alleviates dilution magnetic effect, ensuring high saturated magnetization and effective permeability. The super-thin Al2O3/SiO2 hybrid layer enhances electrical resistance, reducing eddy loss. Effects of the in-situ oxidation time on insulating layer and soft magnetic performances of SMC are investigated in detail. Synchronous reduction of eddy current loss and hysteresis loss is achieved through high resistance accompanied with proper insulating layer thickness and low coercive force provided by the special microstructure. For powder with 90 min oxidation at 500 degrees C, core loss of SMC is low up to 64 mW/cm3 at 50 mT and 100 kHz and 363 mW/cm3 at 100 mT and 100 kHz, while the permeability is kept at 50 until 1100 kHz and is stable until 140 degrees C. Meanwhile, DC bias performance reaches 51.2% at 100 Oe applied field and Q value is 104.8 at 400 kHz.