Preparation And Magnetic Properties Of Fe-Si-Al/Fe-Si Magnetic Powder Cores

The Fe-Si-Al/Fe-Si alloy powder cores are widely used in telecommunication,UPS, power source in solid-state laser, solar electrical energy generation and so on, due to their high saturation magnetization, high resistivity, very low magnetostriction, and relatively low core loss. In this paper, the effects of insulation coating, molding pressure and heat treatment temperature on the magnetic properties of Fe-Si-Al/Fe-Si alloy powder cores were studied.Aluminum sol was coated on the surface of Fe-Si-Al powders by the hydrolysis of Al（NO₃）₃, which was resolved to Al₂O₃ during the heat treatment process. What’s more, Al₂O₃ coating layer has high electrical resistivity and thermal stability, and the lowest core loss of the powder cores were 101 m W/cm3.The manganese oxide coating layer was designed, which improved the resistivity, DC bias stabilityand decrease the core loss of the Fe-Si powder cores. The composition and microstructure of coated powders were XPS, SEM and EDS. The static magnetic parameters of samples were characterized by VSM. The results show that the surface of Fe-Si alloy is evenly coated with the insulating manganese oxides. The thickness of the insulating layer on alloy particles was determined to be in a range of 20–210 nm, depending upon the KMn O4 concentration. Compared with the samples without KMn O4（x=0）, the percent permeability（μ（H）/μ（0））of the samples（x=1.5） increased by approximately 26% and the core loss reduced by 100 m W/cm3（f=50k Hz）.Silica sol/Na₃（PO₃）₃/silica sol coating was designed to optimize the molding pressure and heat treatment temperature. This kind of coating is similar to the "sandwich" structure, which can effectively improve the magnetic properties of Fe-Si magnetic powder cores. Compared to the sample without Na₃（PO₃）₃/silica sol, the percent permeability increased by about 7% and the core loss was decreased by about 25 m W/cm3（f=50k Hz）, when the powders coated in 0.15% Na₃（PO₃）₃.The effect of pressure and heat treatment temperature on the percent permeability of Fe-Si-Al/Fe-Si alloy powder cores was studied. As the pressure increased from 1095 MPa to 1867 MPa, the core loss of Fe-Si-Al alloy powder cores was reduced by about 40 m W/cm3. When the temperature rose from 600°C to 750°C, the core loss was reduced by about 60 m W/cm3.