Soft magnetic properties, microstructure, and growth mechanism of FeSiAl soft magnetic powder cores fabricated via hexafluozirconic acid passivation

In order to develop FeSiAl soft magnetic powder cores (SMPCs) with excellent soft magnetic properties, FeSiAl powder passivated by hexafluorozirconic acid (H₂ZrF₆) was sucessfully prepared and the effect of different concentrations of H₂ZrF₆ on the effective permeability (μ_e) and core loss (P_cv) of FeSiAl SMPCs were systematically studied. H₂ZrF₆ (0.1 wt% of FeSiAl powder) passivation successfully optimized the soft magnetic properties, when the μ_e reached 94, the P_cv was only 180 mW/cm³ at 0.05 T and 100 kHz. SEM, XRD, FTIR, XPS, and TEM were used to investigate the microstructure and growth mechanism of the coating layer. The FeSiAl powder was passivated by H₂ZrF₆ to form a composite coating layer with dominating Fe₂O₃, Al₂O₃, SiO₂, ZrF₄ and a small amount of AlF₃, ZrO₂, while the AlF₃ and ZrO₂ content increased significantly after annealing. In addition, this study effectively improved the high frequency characteristics of FeSiAl SMPCs and analyzed the generation of coating layer, providing a feasible way for the insulation treatment of soft magnetic powder cores.