| Due to its low price and excellent soft magnetic performance,the Fe-Si-Al magnetic powder core was widely used to fabricate magnetic components applied in the fields of power industries,such as switching power supply,power transformer and filter equipments.In this thesis,pure inorganic materials were attempted to realize the insulation coating and bonding of Fe-Si-Al magnetic powder core.And the coating agent,binder and process parameters were investigated for obtaining the Fe-Si-Al magnetic powder core with low loss,high quality factor,excellent DC superposition characteristics and high mechanical strength.Insulation coating is the key process in the production of the Fe-Si-Al magnetic core.In this thesis,phosphoric acid,phosphate and chromic anhydride were used as coating agents,the Fe-Si-Al magnetic powders were insulating coated for one or two times with one or several coating agents.Its surface morphology and corrosion resistance were characterized by the technologies of scanning electronic microcopy（SEM）and Tafel curve.The results showed that after 0.1 wt%CrO3 and 1.0 wt%H3PO4 coating agent was coated on the magnetic powder by the slow drying process,the prepared insulating coating film was uniform,crack-free,and dense with a small amount of crystal salts on the surface of the insulating coating.Compared with the other once-coating insulation films,the insulating coating film can effectively prevent corrosion of NaCl on the matrix,showing the corrosion current of the Tafal curve of 1.758×10-6?A·cm-22 and the corrosion potential of-70 mV.As for the two-times coating film,the results showed that by through the slow drying process,after using 0.1 wt%CrO3 and 1.0 wt%H3PO4 coating agent,subsequently adding Mn（H2PO4）2,the composite insulation coating film was uniform,crack-free and dense with a small amount of crystal salts on the surface of the insulating coating.In comparison with the other two-times coating film,the insulating coating film can more effectively prevent corrosion resistance in NaCl solution,showing the corrosion current of1.534×10-6?A·cm-22 and corrosion potential of-70 mV.The mechanical strength of the Fe-Si-Al magnetic powder core can be significantly increased by the addition of the binder,and its magnetic properties can be adjusted to a certain extent.In this thesis,sodium silicate and aluminum dihydrogen phosphoric are used as the binders.The effects of the content of water glass,filler,modifier and dispersant,P/Al ratio of aluminum phosphate,adding amount,alumina filler content,particle size,dispersant and bonding process parameters were studied on magnetic properties and mechanical properties of Fe-Si-Al magnetic powder core.The results showed that when increasing the mass fraction of water glass used as binder,the L value of the magnetic core inductor was obviously decreased,the magnetic loss Pcvv value showed a slight decreasing trend,and the value of the quality factor Q was increased slightly.The DC superposition characteristic of the magnetic powder core was optimized,and the mechanical strength of magnetic core was enhanced.When the content of water glass is 2 wt%,the magnetic powder core inductance L was determined to be 30.38μH,the direct-current superposition Dc to be 22.42μH,the quality factor Q to be 73,the magnetic loss Pcvv to be 195 mW/cm,the magnetic powder core blank strength F1 to be 173 N,and the magnetic core sintering intensity F2 to be 231 N.When the sodium silicate was replaced by sodium fluosilicate,the magnetic properties of the magnetic core was almost not affected,but its mechanical strength was increased obviously.When the content of modified sodium silicate was 2 wt%,the strength of magnetic core blank was measured to be 238 N,and the sintered strength of magnetic core to be 333 N.The addition of sodium hexameaphosphate or sodium tripolyphosphate dispersant had no obvious effect on the magnetic and mechanical properties of magnetic core.When using Al（H2PO4）3 as binder,the magnetic properties of magnetic powder core had not been affected,but when P/Al>3,the blank strength of the magnetic powder core was measured to be 260 N,and the strength after firing to be 422 N,which was much greater than that of Al（H2PO4）3（P/Al<3）.With the increase of the mass fraction of Al（H2PO4）3（P/Al>3）,the decrease of the L value of the magnetic core inductor is obvious,the Pcvv value of magnetic loss shows a slight decreasing trend,the value of the quality factor Q increases,but the increase is small,the DC superposition characteristic of the magnetic powder core is optimized and the mechanical strength of magnetic core is enhanced.When the content of Al（H2PO4）3 is 2 wt%,the magnetic powder core inductance L was measured to be 30.03μH,the direct-current superposition Dc to be 22.79μH,the quality factor Q to be 77,the magnetic loss Pcvv to be 184 mW/cm,the magnetic powder core blank strength F1to be 260 N,the magnetic core sintering intensity F2 to be 422 N.The addition of fillering Al2O3 powder had no obvious effect on the magnetic properties of magnetic cores,but significantly improved the mechanical strength of magnetic cores.When 0.2 wt%Al2O3powder was added as the filler,the blank and burned strength of magnetic powder core was increased from 189 and 224 N to 342 and 460 N,respectively,compared with no alumina powder.With the added Al2O3 powder was increased from 0.2 wt%to 0.6 wt%after the coated magnetic powder,there was no obvious change in mechanical strength of Fe-Si-Al magnetic powder core.The particle size of Al2O3 powder and dispersant of Al2O3 powder had no obvious effect on the magnetic and mechanical properties of magnetic core.It was found that the bonding process had a certain effect on the performance of magnetic core.With prolonging aging time,the mechanical strength of magnetic core was incrreased.When the aging time was longer than 5 min,the strength of magnetic core was more than 400 N after burning.Room temperature stirring time（5-20 min）and static time（0-120 min）had no obvious effect on the performance of magnetic power core. |
