| With the rapid development of information,electromagnetic pollution has been produced by electronic equipment,which not only causes the damage of devices but also endangers human health.In recent years,electromagnetic shielding is considered to be the most effective method to solve electromagnetic pollution.Among many electromagnetic shielding materials,Cu-Fe alloys have great application potential,which can be widely used in aerospace,electronic communication and other fields.However,there are few studies on electromagnetic interference shielding properties of Cu-Fe alloys at present.Therefore,the effects of Cu/Fe mass ratio,heat treatment temperature and preparation process,as well as the type and morphology of iron powder on the conductivity,magnetic properties and electromagnetic interference shielding properties of Cu-Fe alloys were systematically studied in this paper.In addition,the shielding effect of Cu-Fe alloys on electromagnetic waves was collaboratively improved in the frequency range of 30 MHz～1.5 GHz.The shielding mechanism of Cu-Fe alloys is also discussed.The main research results are as follows:(1)Cu-Fe alloys with various mass ratios were prepared by hot pressing sintering and then hot rolling.The effects of Fe content on microstructure,electrical conductivity,magnetic properties and electromagnetic interference shielding properties of Cu-Fe alloys were systematically investigated.The results show that: the Cu-Fe alloys prepared by the two-step method is mainly composed of α-Fe and Cu phases,where the Fe phase is evenly distributed.The electrical conductivity of Cu-Fe alloys decreases with the increase of Fe content.Meanwhile,the saturation magnetic induction increases as Fe content increases.In the range of30 MHz～1.5 GHz,the Shielding Effectiveness(SE)of Cu-Fe alloys decreases with the increase of Fe content.Especially in the high frequency region,SE decreases significantly with the increase of frequency.Cu-20 Fe alloys exhibit excellent electromagnetic interference shielding properties in the test frequency range due to its good electrical conductivity and magnetic properties,the SE value of which can reach 105～113 d B.The electromagnetic interference shielding properties of Cu-Fe alloys are mainly influenced by the electrical and magnetic properties,and the electromagnetic shielding mechanism is mainly composed of reflection,absorption and conductance loss.(2)The effects of the annealing temperature on microstructure,electrical conductivity,magnetic properties and electromagnetic interference shielding properties of Cu-20 Fe alloys were investigated.The results show that: with the increase of annealing temperature,the average grain size of the alloys increases while the stress decreases in the process of heat treatment.Then,the electron scattering decreases,resulting in the increase of the electrical conductivity and magnetic properties.However,when the annealing temperature reaches 900℃,fine grains appear with uneven distribution.Additionally,the electrical conductivity and magnetic properties of the Cu-20 Fe alloys decrease to a certain degree.Cu-20 Fe alloys at annealing temperature of 700℃ has the best electromagnetic interference shielding properties,and its SE value can reach 107～116 d B.Therefore,700℃ is chosen as the optimum annealing temperature for Cu-20 Fe alloys.(3)The effects of the preparation process on the microstructure,electrical conductivity,magnetic properties and electromagnetic interference shielding properties of Cu-20 Fe alloys were studied.The results show that: compared with the hot-pressing state,the average grain size of the Cu-20 Fe alloys in the hot rolling state increases.However,the small Angle grain boundary,deformation structure and stress also increase significantly,which result in the decrease of the electrical conductivity and magnetic properties of the alloys.After annealing,the average grain size further increases,and the small Angle grain boundary,deformation structure and stress decrease obviously owing to the recrystallization process,so that the electrical conductivity and magnetic properties of Cu-20 Fe alloys increase obviously in comparison with that of hot rolling state.The improvement of electrical conductivity and magnetic properties can further increase the reflection,absorption and conductance loss of electromagnetic wave,making the Cu-20 Fe alloys achieve the best electromagnetic interference shielding properties.(4)The effects of the type and morphology of iron powder on the microstructure,electrical conductivity,magnetic properties and electromagnetic interference shielding properties of Cu-20 Fe alloys were investigated.The results show that: the electrical conductivity,magnetic properties and electromagnetic interference shielding properties of Cu-20 Fe alloys prepared by high purity iron powder are better than those prepared by reduced iron powder and carbonyl iron powder,which can be attributed to the difference of properties of iron powder.Compared with the spherical and fibrous carbonyl iron power,the contact mode of surface to surface between the internal phases was displayed in the Cu-20 Fe alloys prepared by flake carbonyl iron powder.Then,the conductive network increases,leading to the electrical conductivity reaching 41.1599%IACS.Meanwhile,flake carbonyl iron powder has high aspect ratio,magnetic loss and anisotropy,which can restrain eddy current loss,improve the absorption of electromagnetic wave and break Snoek limitation.Therefore,in the frequency range of 30MHz～1.5 GHz,the Cu-20 Fe alloys prepared by flake carbonyl iron powder has the best electromagnetic interference shielding properties,and its SE value can reach 110～117 dB. |
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