Effect Of Heat Treatment And Rare Earth Elements On Electromagnetic Shielding Effectiveness Of Mg-Zn-Zr Magnesium Alloy

With the rapid development of electrical and communication industry, Electromagnetic interference （EMI） caused by electromagnetic （EM） radiation areincreasingly doing great harm to information security of various countries and thehealth of human being. Thus, there is a critical need to develop effective and practicalEMI shielding materials in order to make the electro-magnetic environment safer andincrease the lifetime of electronic devices. Traditionally high conductivity, magneticpermeability metallic materials and polymer composites are by far the commoncandidates for EMI shielding materials. Nevertheless, traditionally high conductivity,magnetic permeability metallic materials and polymer composites suffer from theirheavy weight, low mechanical property, respectively, which restricts some of theirapplications. It is well known that magnesium alloys possess not only low density, highspecific stiffness, high specific strength, but also have relatively good conductivity andhigh shielding capacity. In this sense, magnesium alloys may be considered as apotential candidate for EMI shielding materials. However, the reports on the EMIshielding characteristics of magnesium alloys are quite limited.This paper focus on obtaining the optimal heat treatment and composition alloywhich have a high EMI shielding characteristics by performing the different types ofheat treatments and adding the different contents of rare earth elements Ce and Y intothe Mg-Zn-Zr alloy. The influence of heat treatment and rare earth elements Ce and Yon EMI shielding characteristics of Mg-Zn-Zr alloy at different states was investigatedby using metallurgical phase analysis, XRD analysis, SEM analysis, EDS analysis,tensile testing, microhardness measurement, electrical conductivity, EMI shieldingeffectiveness testing and so on. Following research results were obtained.①Heat treatment has an evident influence on EMI shielding property ofas-extruded Mg-Zn-Zr magnesium alloy. Direct artificial aging（T5） and artificial agingfollowing solid solution（T6） result in an considerable improvement of shieldingcapacity in the testing frequency range of30-1500MHz. Solid solution at400℃for5h and subsequent artificial aging at170℃for25h and direct artificial aging at150°Cfor15h can be considered as the optimum T6and T5heat treatment, respectively, whichhave an evident raise on EMI shielding property of as-extruded Mg-Zn-Zr magnesiumalloy. The shielding effectiveness （SE） of the Mg-Zn-Zr alloy are significantly improved to62-75dB and70-80dB in these two optimum conditions，respectively. At the sametime, the alloys in these conditions possess favorable mechanical properties. EnhancedEMI shielding capacity in Mg-Zn-Zr magnesium alloy induced by T5and T6heattreatment could be dominantly attributed to the increase of electrical conductivity, which mainly originates from the precipitation of numerous second phases. However,the coarsening of precipitates reduced their shielding contribution.②Rare earth element Ce has an obvious effect of refining crystal grains ofMg-Zn-Zr magnesium alloy and forms a new Mg-Zn-Ce ternary phase. The structureuniformity of alloy with different Ce addition is different after hot extrusion. When Ceaddition is1%, the structure uniformity is the optimum. Adding0.5%³%Ce canenhance the EMI shielding effectiveness of as-extruded Mg-Zn-Zr magnesium alloy,especially the SE of the alloy with1%Ce are significantly improved to70-82dB. Andthe above mentioned alloy possesses favorable mechanical properties. The subsequentartificial aging at150℃for25h can further increase the SE of the alloy with1%Ce to78-89dB. Improved EMI shielding capacity in Mg-Zn-Zr magnesium alloy induced byrare earth element Ce could be dominantly depended on the increase electricalconductivity and the enhancement structure uniformity. The increase of electricalconductivity mainly originates from the numerous Mg-Zn-Ce ternary phases.③Rare earth element Y has a small effect of refining crystal grains of Mg-Zn-Zrmagnesium alloy and forms a new Mg-Zn-Y ternary phase with Mg, Zn.When Yaddition is1%, the ternary phase of alloy is mainly W-Mg₂Y₂Zn₃phase and I-Mg₂YZn₆phase, whereas when Y addition4%, the ternary phase of alloy is mainly W-Mg₂Y₂Zn₃phase. Adding1%⁴%Y can enhance the SE of as-extruded Mg-Zn-Zr magnesium alloy.And as the Y addition increases, the SE increases, whereas the mechanical propertiesreduce. Therefore, the combination property of the alloy with1%Y is the optimum. Thevalue of SE and tensile strength is improved to75-92dB and321MPa, respectively.Improved EMI shielding capacity in Mg-Zn-Zr magnesium alloy induced by rare earthelement Y could be due to the numerous Mg-Zn-Y ternary phase, which strengths theattenuation of electromagnectic wave.