Relationship between the Microstructure and Magnetic Properties of Fe-Si-Cr Powder Cores

Magnetic components prepared using Fe-Si-Cr alloy powders have been widely used in high-current power inductors due to their high initial permeability, high-saturation magnetization, and excellent dc-bias characteristics. Fe-Si-Cr alloy bodies were prepared in this paper using a uniaxial molding press at different compaction pressures. Samples were then annealed at different temperatures to form a chromium-rich oxide insulating layer on the powder surface to reduce the core loss. The compaction pressure and the annealing temperature effects on the microstructure, internal strain, and insulating layer thickness and the electromagnetic properties for Fe-Si-Cr alloy powder compacts were investigated. The results showed that the relative density gradually increased with increasing compaction pressure, leading to increased saturation magnetization, thereby improving the initial permeability from 29 to 37. After annealing, the internal strain was reduced, which resulted in the initial permeability increasing substantially. Moreover, the electric resistivity and dc-superposition characteristics also increased with increasing heat treatment temperature. However, excessively thick insulating layer formed on the Fe-Si-Cr alloy powder surface resulting from annealing at too high temperature leading to initial permeability and saturation magnetization degradation.