Insulation Layer Design And Powder Doping Process For Fe-based Soft Magnetic Composites And Its Influence On Soft Magnetic Properties

Soft magnetic composites（SMCs）have been widely used in the preparation of key magnetic components in power electronics industry because of their unique properties,such as relatively low core loss under medium and high-frequencies,favorable anti-saturation characteristic,good frequency stability and flexible design with high-dimensional accuracy.To further reduce the core loss of SMCs and improve their corresponding electromagnetic performance,so as to satisfy the development needs of miniaturization,high-frequency and high-power application for power electronic devices.In this work,a three-dimensional loss separation fitting model was first established for the Fe-based SMCs.And then,the regulation mechanism of comprehensive soft magnetic properties by designing powder insulation layer and doping micron-sized powders for the Fe-based SMCs has been systematically analyzed under the comprehensive consideration of the preparation process conditions of insulation coating.Finally,an insulating coating process for industrial products of SMCs was proposed,and it is pointed that the microstructure design of magnetic powder in the SMCs based on doping process was an important way to further improve the comprehensive soft magnetic properties of SMCs.The main research results are as follows:（1）The comprehensive soft magnetic properties of FeSiSMCs insulated with different materials,including silicone resin,inorganic Si O₂and Ti O₂,soft magnetic Ni Zn-ferrite and composite coating of inorganic-magnetic layer,has been compared and analyzed.As compared to the other insulating materials,the SMCs insulated with the composite coating exhibited relatively good comprehensive soft magnetic properties,but possess two obvious shortcomings of long total preparation time exceed 110 min and high synthesis temperature of 80℃;the SMCs insulated with inorganic material exhibited a better DC-bias with higherμ′@7960 A/m=44.6,a relatively low P_cvof 1040.6k W/m³at 100 k Hz,0.1 T,and can be fabricated at room temperature with a total preparation time of 70 min,which is favorable for being widely used in industry.（2）For the Ni Zn-ferrite coating,with the increase of coating amount,theμ’of Fe Si SMCs increased first and then decreased,while the corresponding P_cvshowed a completely opposite trend.Among this,the Fe Si SMCs insulated with 1.0 wt.%of Ni Zn-ferrite exhibit a relatively high permeability of 84.3 and low P_cvof 1036.5 k W/m³at 100 k Hz,100 m T.The fitting power coefficients of P_h～B_m,P_exc～f,and P_exc～B_mfor the Ni Zn-ferrite coated SMCs are in the ranges of 1.96～2.02,1.52～1.67 and 1.80～1.84,respectively.（3）For the inorganic SiO₂coating,theμ’andμ’@7960 A/m of FeSiBCCr amorphous SMCs showed a slow decreasing trend with the increasing addition of the precursor TEOS,while the corresponding P_cvdecreased first and then increased.Among this,the Fe Si BCCr amorphous SMCs insulated under the TEOS concentration range of0.09～0.14 m L/g exhibit excellent comprehensive soft magnetic properties of a relatively highμ′of 67.5,an good DC-bias property ofμ′@7960 A/m=46.2,and a low P_cvof 765 k W/m³at 200 k Hz,80 m T.（4）Due to the fact that the SMCs insulated with Ni Zn-ferrite or SiO₂coating above possess a relatively high bulk electrical resistivity of 1.22～2.8Ω·m,the corresponding inter-part eddy current loss P_e^interis only 1/600～1/250 of P_cv,thus has almost no effect on the change of P_cv.Meanwhile,a stableμ′even increasing the frequency up to 3 MHz can also be obtained for the well-insulated SMCs above.（5）In view of the disadvantages of vast non-magnetic pores in the SMCs prepared from water atomized Fe Si BCCr amorphous powders and poor DC superposition property of Fe-based nanocrystalline（Finemet）SMCs,the influence law and regulation mechanism of powder microstructure inside SMCs on their magnetic properties were investigated based on the doping process of micron-size Fe Si powders.Doping appropriate content of the smaller Fe Si powders will fill the non-magnetic pores between magnetic particles with larger particle size,which is conducive to the improvements of compact density and soft magnetic properties for the SMCs.When doping excessive micron-size Fe Si powders,however,the aggregation in the SMCs will occur,leading to the damage in magnetic properties of SMCs.The Fe Si BCCr/Fe Si compound SMCs doped with 12 wt.%Fe Si powders and the Finemet/Fe Si compound SMCs doped with the Fe Si powders in the range of 10～14 wt.%exhibited better comprehensive soft magnetic properties as compared to the cases doped with other contents of Fe Si powders.（6）The influence of interblending the Fe Si and FeSiAl powders with each other with the introduction of the impact of powder size matching on the Fe Si Al/Fe Si compound SMCs were systematically analyzed.The Fe Si400↑/Fe Si Al400↓（within mass ratio of 7:3）compound SMCs are conducive to raising theμ_eby 12.6%and reducing the P_cvby 17.5%at the expense of 2.0%reduction inμ_e@7960 A/m as compared to these of normal Fe Si SMCs.The the Fe Si Al600↑/Fe Si600↓（within mass ratio of 7:3）compound SMCs exhibit excellent magnetic properties of separately increasing theμ_eandμ_e@7960A/m by 3.1%and 12.8%at the cost of increasing the P_cvonly by 3.2%compared with these of common Fe Si Al SMCs.The above research results will expand the understanding of the regulation mechanism of electromagnetic characteristics of SMCs,and will further promote the market application of Fe-based SMCs,which meets the development needs of power electronics industry.