Microstructure, formation mechanism and magnetic properties of Fe1.82Si0.18@Al2O3 soft magnetic composites.

• FeSiAl@Fe 3 O 4 core-shell structure was formed by NaOH oxidation. • Fe 1.82 Si 0.18 @Al 2 O 3 SMCs were obtained by SPS. • Effects of oxidation time on the microstructure and formation mechanism were investigated. • Enhanced magnetic permeability stability, high resistivity and low magnetic loss. Fe 1.82 Si 0.18 @Al 2 O 3 soft magnetic composites (SMCs) have been fabricated by NaOH oxidation combined with subsequent spark plasma sintering (SPS). The microstructure and generation mechanism of Fe 3 O 4 coatings on the surface of FeSiAl powders have been investigated systematically. Effects of oxidation time on the magnetic properties also have been revealed. In addition, the displacement reaction between Fe 3 O 4 and Al during SPS process results in the formation of Al 2 O 3 insulation layer, leading to a remarkable variation of the magnetic performances of SMCs. The increased NaOH oxidation time had positive influences on the electrical resistivity, frequency stability of permeability and core loss. The saturation magnetization first decreases then increases with the increase of oxidation time. These above results indicate that the fabrication method in this paper creates a way to form Fe 3 O 4 nanoparticles and Al 2 O 3 insulation layer, which enhance the magnetic performance of FeSiAl SMCs and will facilitate the design of efficient magnets in the future. [ABSTRACT FROM AUTHOR]