| With the popularization and application of 5G communication technology,more and more electronic devices have been put into use,electromagnetic radiation pollution and electromagnetic shielding have received more and more attention,and the development of efficient electromagnetic shielding materials has become a research hotspot in recent years.Magnesium alloy is a very potential electromagnetic shielding material,especially in the current pursuit of flexible and lightweight electronic equipment,magnesium alloy has good mechanical properties and excellent physical properties such as light weight and high strength,and has a good application prospect in the field of shielding materials.In this study,0.05 mm and 0.1mm pure Mg,AZ31,AZ61 and LZ91 foil are obtained by rolling.The shielding properties of the foil are measured and compared in the full frequency band of 300 MHz to 18000 MHz.The influences of thickness,conductivity,grain size and other factors on the shielding efficiency of the foil are analyzed.4 kinds of 0.1mmfoil are annealed under different conditions,the shielding efficiency is compared,and the influence of different annealing processes on shielding efficiency is analyzed.Finally,the application prospects of different foil materials in different frequency bands are discussed.The main results are as follows:The testing foil shielding efficiency generally increases with the increase of electromagnetic wave frequency,and when the frequency of electromagnetic wave increases,the skin depth will gradually decrease,that is,the electromagnetic wave is more easily shielded by the foil.The shielding efficiency curve of magnesium alloy foil in the frequency band of 10000 MHz to 18000 MHz tends to be stable,and the shielding efficiency is saturated,maintaining at about 115 d B.In the 30 MHz to 18000 MHz band measurement of the rolled alloy foil,0.1mm AZ61 foil shows the best shielding efficiency,and the overall average shielding efficiency reaches 108 d B.Comparing the shielding efficiency results of rolled pure Mg,AZ31 and AZ61 magnesium alloy,because there is more Al content in AZ61 magnesium alloy,more second phase can be formed,and the grain growth can be inhibited.The grain size in rolled state is the smallest,and the number of grain layers in the thickness direction of the foil is the largest.Therefore,the shielding efficiency of AZ61 foil in rolled state in this study is the best.Different annealing processes have different effects on shielding efficiency of foil.After recrystallization annealing,the broken grains in rolling state become complete grains,the internal defects are reduced,but the high annealing temperature and long annealing time lead to the grain growth and the grain boundary area is reduced.For pure Mg foil,annealing treatment improves the overall shielding efficiency in the measured frequency band,and the best shielding effect is the sample annealed at 100 ℃ for 1 h,with an average shielding efficiency of 108 d B,because annealing treatment eliminates part of the stress in pure magnesium,reduces internal defects,thereby improving the conductivity and conducive to the conduction of electromagnetic waves.The absorption loss of pure magnesium foil is enhanced,and the shielding efficiency is improved.For AZ31 foil,annealed at 150 ℃ for 1 h,the overall shielding efficiency is the best,and the average shielding efficiency is 109 d B.This is because stress-relieving annealing eliminates part of residual stress,restores the structural characteristics of the material itself,and improves the reflection and absorption ability of the material for electromagnetic waves.AZ61 foil annealed at300 ℃ for 1 h has the best overall shielding performance in the measured frequency band,and the average shielding performance is 109 d B.For LZ91 foil,the shielding efficiency of LZ91 foil under different annealing conditions in different frequency bands has its advantages and disadvantages.The sample annealed at 100 ℃ for 1 h has the best overall shielding efficiency in the test frequency band,and the average shielding efficiency is 106 d B.The above research results on the electromagnetic shielding properties of magnesium alloy foil will provide reference for the development of new lightweight and flexible electromagnetic shielding materials in the future. |
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