Surface Modification of Ultra-Thin Flaky Fesial Powders by Heat Treatment with Excellent Magnetic Properties

Abstract

The ultra-thin flaky FeSiAl powders with a thickness of 0.65 μm were treated by low-temperature oxidation and high-temperature reduction in order to modify their surface properties, respectively. An inherent outer layer mainly composed of Fe2O3, SiO2-Al2O3, and Al2O3 existed on the surface of the original FeSiAl powders. The oxidation treatment led to the increase of Fe2O3 content in the outer layer. During the reduction treatment, H2 only ensured that no excessive oxidation occurred, an aluminothermic reaction mainly occurred to form Al2O3. During the pressing process for the magnetic core, the flaky FeSiAl powders naturally arranged into a stack structure with (100) orientation. All magnetic cores exhibited excellent magnetic performance. The effective permeability of the FeSiAl magnetic core after reduction treatment was as high as 694 at 100 kHz, and which total loss reached 108.8 mW/cm3 and 977.5 mW/cm3 under maximum applied fields of 50 mT and 150 mT at 100 kHz, respectively. By the loss separation, it was found that the hysteresis loss in total loss accounted for around 80% for all samples at 50 mT and 100 kHz, and the surface modification by heat treatment mainly inhibited the hysteresis loss. These results revealed the key role of reducing the thickness of flaky FeSiAl powders in further improving their magnetic core properties.

Keywords: Flaky FeSiAl, Magnetic core, surface modification, heat treatment