| With the development of modern science and technology, various kinds ofelectrical and electronic equipment brought convenience to the human production andlife. However, these electrical and electronic equipments generate electromagneticradiation during work which threatens human’s health and the natural environmentseriously. At the same time, with the development and applicant of various high-techmilitary products, the security problems caused by information leakage throughelectromagnetic wave will threaten to the country’s political, economic, military anddiplomatic interests and security. It will cause immeasurable losses. As a result, theresearch and development of high-performance electromagnetic shielding materials isone of the focuses of attention at home and abroad.Magnesium alloy is the lightest metal structural materials in the engineeringapplication. It has many advantages, such as high specific strength, damping, machiningperformance and excellent electromagnetic shielding property and so on. Comparedwith traditional metal shielding materials, magnesium alloy is lighter. And magnesiumalloy can apply as structural material which is lack in the metal coating andpolymer-matrix shielding materials. What’s more, magnesium alloy is the greenengineering material which is friendly to the environment. However, the research ofelectromagnetic shielding property of magnesium alloy is limited. Nowadays,magnesium alloy has applied to mobile phones, computers and other3C products.These electronic products will produce electromagnetic radiation, which is harmful tohuman health. Therefore, the research of electromagnetic shielding property ofmagnesium alloys appears very necessary. As a kind of wrought magnesium alloys withgood plastic deformation ability, AZ magnesium alloy is widely used. The changes ofgrain size, twin, dislocation, texture and the second phase during the plastic deformationand heat treatment will affect the electrical conductivity of magnesium alloys whichleads to the change of electromagnetic shielding property. Therefore, a systematic studyof the influence of deformation and heat treatment on electromagnetic shieldingproperty and shielding mechanism of AZ magnesium alloy will broaden the applicationof magnesium alloy as electromagnetic shielding material and reduce the harm ofelectromagnetic radiation. Metallographic observation, scanning electron microscopy observation, XRDanalysis, microhardness measurement, electrical conductivity measurement,electromagnetic shielding property measurement and tensile testing at room temperatureetc. were used in this study. The electromagnetic shielding property of magnesium alloyand the influence of grain size, rolling deformation, rolling temperature and agingtreatment on the electromagnetic shielding property of AZ31and AZ61magnesiumalloy were investigated. Following research results were obtained.①The electromagnetic shielding property of pure magnesium is great.Electromagnetic shielding effectiveness of pure magnesium with2mm thick is50~70dB in the testing frequency range of30~1500MHz, which is obvious higher than purealuminum with the same tickness. The sequence of electromagnetic shielding propertyfrom high to low is AZ31, AZ61, ZK60, ZM61.②The effect of grain size on the electromagnetic shielding property of AZ31alloyis great. The electromagnetic shielding property decreases gradually with the graingrowing up. This is due to the diminution of the multiple reflection attenuation (B) andabsorption attenuation (A) induced by the decrease of grain boundary.③A slight change in shielding property occurs after small reduction hot rolling. Asignificant increment in shielding effectiveness of hot rolled AZ31alloy with largereduction is achieved. The AZ31alloy with57%reduction exhibits good shieldingproperty with the shielding effectiveness value from63dB to82dB. This is attributed tothe increase of absorption attenuation (A) and multi reflection attenuation (B) inducedby grain refining and reflection attenuation (R) induced by the strong {0001} basaltexture.④Electrical conductivity and electromagnetic shielding property of AZ61alloyextruded sheet improve significantly after hot rolled at325℃. As the deformationtemperature increasing, the properties decrease gradually. The properties increase againafter hot rolled at400℃. The AZ61alloy rolled at325℃exhibits good electromagneticshielding property and mechanical property:87～94dB for electromagnetic shieldingproperty,394MPa for tensile strength and267yield strength. The improvement ofelectromagnetic shielding property and mechanical property is significant.⑤The second phase precipitate obviously during aging at200℃.The secondphase volume fraction of AZ61magnesium alloy increases gradually andelectromagnetic shielding property also gradually rise as the aging time extended. Theshielding effectiveness of AZ61magnesium alloy extrusion sheet up to71～84dB after aged for100h. This is mainly attributed to the increase of reflection attenuation (R) andabsorption attenuation (A) induced by improvement of electrical conductivity whichcaused by the alloy elements precipitate as the second phase from supersaturatedmagnesium matrix. |
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