Study On Electromagnetic Shielding Properties Of Magnesium Alloys

The electromagnetic radiation pollution is increasingly serious for an increasing number of electronic products and electrical equipments. Therefore, effective shielding materials are in urgent need of development. When magnesium alloy used as shielding materials, compared with the traditional metals, it has low density, light weight and the advantage of high strength. Compared with foam, coating, composite materials, it has good mechanical property, and electromagnetic shielding performance. Magnesium alloy is friendly to the environment, also can be used as engineering structure materials. However, the research on magnesium alloy electromagnetic shielding performance is very limited and the influencing factors and related shielding mechanism is not clear.Flange coaxial combined with vector network analyzer system, was used to test the shielding effectiveness of magnesium alloys in 30 ~ 1500 MHz frequency range. Effect of alloy elements on electromagnetic shielding performance of binary and ternary alloy were studied; effect of grain size, texture, and second phases on electromagnetic shielding performance of various magnesium alloys were investigated; theoretical calculation of electromagnetic shielding effectiveness of magnesium alloys has carried on and compared with experimental results; design scheme of high shielding performance of magnesium shielding materials was put forward. Thesis research results will be conducive to the magnesium alloy materials in the application in the field of electromagnetic compatibility and also has important theoretical reference value and significance for engineering applications. The main results are following:① In as-cast and solid solution state, the conductivity of five group of binary alloys were gradually reduced with the increase of the component, electromagnetic shielding effectiveness decreased with the increase of the test frequency. The " specific electrical resistivity "(which is the incensement of resistivity caused by adding one atomic percentage of solute atoms) of solid solution atoms in magnesium alloy and its effect on the electromagnetic shielding properties of magnesium alloys meet the following orders: Zn < Al < Sn < Y < Gd. The specific electrical resistivity, ΔV/VMg, valency, configuration of extra-nuclear electron of the five solute elements ware the main cause of the discrepancy.② In ZA alloys, the electrical conductivity of alloys increased with Zn/Al ratio. In ZW alloys, the electrical conductivity of alloys decreased with Y/Zn ratio. Order of alloy elements on the influence of the conductivity of ternary magnesium alloy was Zn < Al < Y. When the incident electromagnetic wave at low frequency band, the electromagnetic shielding effectiveness of ZA and ZW series alloys were consistent to their conductivity change tendency. When the incident electromagnetic wave at high frequency range, the electromagnetic shielding performance of ZA and ZW series alloys were fluctuated with the incensement of second phase content and tend to be stable.③ The grain size of magneium alloy increased significantly. This greatly decreased the grain boundary area inner alloy, which caused less more incident electromagnetic wave were multiply reflected and induced the decrement of SEB. However, the decrease rate was tiny and usually can be ignored. Basal texture developed, then significantly increased the shielding effectiveness of magnesium alloys. It mainly due to the increasing of SER. During the whole process, the grain size and texture had no effect on the e absorption loss(SEA).④ The second phase in Mg alloy is intermetallic compound, which is usually treated as an insulator. The type of second phase has little effect on electromagnetic shielding performance. The content of second phase has great effect on shielding performance, especially in high frequency range. Too much second phases will lead to reduce of conductivity, thus will decrease electromagnetic shielding performance. The second phase content for the high shielding performance exists an optimal value. Homogeneous precipitation in aging state are efficiency in attenuation of the incident electromagnetic wave than the along grain boundary second phase in as-cast state. The second phase in magnesium alloy orientation distribution in perpendicular to the electromagnetic wave incident direction, compared to other distribution of second phase, can more effective in attenuation of incident electromagnetic wave, thus improve the electromagnetic shielding performance of the alloy.⑤ Equivalent transmission line shielding theory can only qualitative forecast the electromagnetic shielding effectiveness. The difference between theoretical shielding effectiveness and laboratory test results is very large, which is increased with the rise of incident electromagnetic wave frequency. The design of high electromagnetic shielding effectivensss of magnesium alloy should condider the adding elements, texture and second phases etc.