Optimization Of Microwave Absorption Properties Of FeSiAl Alloy Soft Magnetic Materials By Heterogeneous Interface Construction

With the development of high-speed communication and the rapid growth of electronic products,the problem of electromagnetic radiation pollution is becoming increasingly serious.Absorbing material has important application value in solving electromagnetic radiation pollution.In the field of military application,stealth technology plays an important role in modern warfare,and absorbing material is one of the most important components of stealth technology and an important research and development topic of modern national defense science and technology.FeSi-based alloy micropowder is one of the most widely used absorbing material,FeSiAl is often chosen as a good absorber because of its high magnetic permeability.However,the permeability of spherical FeSiAl soft magnetic alloy powder is limited by the Snoek limit,and FeSiAl alloy powder also has large dielectric constant,which leads to poor impedance matching.In this thesis,FeSiAl soft magnetic alloy powder atomized by water was used as the matrix material,and a series of methods were gradually adopted to improve the absorption performance:the shape anisotropy was gradually improved by ball milling,the impedance matching of the material was improved by oxidation heat treatment,and the polarization characteristics were enhanced by MOFs material compounding.Then,through carbonization heat treatment,the heterostructure interface was constructed to enhance polarization and multiple reflection/scattering,and finally FeSiAl soft magnetic composite materials with excellent microwave absorption performance were obtained.The shape anisotropy of flaky FeSiAl soft magnetic alloy powder prepared by ball milling is optimized,which breaks through the Snoek limit.The complex dielectric constant and complex permeability are improved,while the electromagnetic wave loss ability of the material is also enhanced,and the wave absorption performance of the material is improved.The minimum reflection loss(RL_min)of flaky FeSiAl soft magnetic alloy powder reaches-49.9 d B at the frequency f of 13.24GHz,and the corresponding absorbing coating thickness d is 1.76 mm,and the effective absorbing bandwidth is also obviously broadened.Then,the flaky FeSiAl soft magnetic alloy powder was oxidized by heat treatment.By controlling the oxidation reaction,the microstructure with oxidized phase dispersed on the surface of FeSiAl soft magnetic alloy was formed on the surface.After oxidation heat treatment,FeSiAl soft magnetic alloy powder not only improves its wave-absorbing performance,but also enhances its environmental adaptability and service characteristics due to the passivation effect formed by oxidation treatment.Metal-organic framework（MOFs）materials have the characteristics of large specific surface area,large pore volume and clear pore size distribution,and they have also attracted attention in the field of absorbing materials.In this thesis,Fe-MOF（MIL-101（Fe））is in-situ compounded with oxidized FeSiAl soft magnetic alloy powder,and the microstructures of FeSiAl soft magnetic material matrix,oxide layer and MIL-101（Fe）cladding layer are coordinated and controlled,and the polarization characteristics and electromagnetic wave loss mechanism are analyzed.When 30 wt%MIL-101（Fe）is compounded with flaky FeSiAl oxidized at 600℃,the RL_min reaches-71.5 d B at the frequency of 5.68 GHz,and the coating thickness is 3.85 mm.The frequency band width of RL≤-20 d B is also significantly increased.The microwave absorbing performance of MIL-101（Fe）@FeSiAl composites is improved by balancing electromagnetic wave attenuation ability and impedance matching.Finally,the MIL-101（Fe）derivatives@FeSiAl composite were formed by high-temperature carbonization heat treatment of the MIL-101（Fe）@FeSiAl composites.The microwave absorbing properties of samples with 20wt%MIL-101（Fe）@FeSiAl carbonized at 600℃,30wt%MIL-101（Fe）@FeSiAl carbonized at 700℃and 40 wt%MIL-101（Fe）@FeSiAl carbonized at 500℃and 600℃were improved.and the heterostructure interface was constructed by MIL-101（Fe）derivatives.The improved microwave absorption performance is mainly due to the formation of heterostructure interface,which enhances the interface polarization and dipole polarization of materials,and improves the multiple loss ability of electromagnetic wave.Suitable impedance matching is also the key factor for improving the microwave absorption performance of MIL-101（Fe）derivatives@FeSiAl composites.In this thesis,the controllable preparation of FeSiAl soft magnetic composite absorbing materials is realized by means of heterogeneous interface construction and microstructure regulation.The research method opens up a brand-new idea for more high permeability soft magnetic alloy materials with well-regulated composition and microstructure to be applied in the field of absorbing materials.The research results have certain economic value and practical significance for solving the problem of electromagnetic pollution,the rapid development of electronic industry and the development of national defense industry.