| Magnesium alloy is the lightest structural metal in industrial application at present.It has the advantages of light quality and high strength.At the same time,magnesium alloy has very good electromagnetic shielding performance.It has lower density than traditional metal shielding materials.Compared with polymer shielding materials,it can get good shielding effect without conducting conductive treatment.It is a kind of potential electromagnetic shielding material.Due to the addition of two kinds of rare earth elements Gd and Y,heat resistance and high temperature mechanical properties of Mg-13Gd-4Y-2Zn-0.5Zr magnesium alloy has been effectively enhanced.Hot working is often required before the alloy is put into practical application.In order to understand the effect of hot working process on the shielding effectiveness of the alloy,the paper has carried on the thermal deformation and heat treatment experiments,and combining with OM,SEM,XRD,tensile test at room temperature,conductivity test at room temperature and shielding effectiveness test etc.The influencing laws and mechanism of deformation temperature,direct aging and solution aging on the electromagnetic shielding performance of the rare earth magnesium alloy are studied.The main conclusions are as follows:(1)The electromagnetic shielding efficiency of cast rare earth magnesium alloy can reach 80.3 to 101dB(30~1500MHz),which is superior to that of pure magnesium metal,AZ31 magnesium alloy,ZM61 magnesium alloy and ZK60 magnesium alloy.The difference in the shielding performance of the alloy caused by the deformation temperature is more pronounced in the medium-high frequency(600 to 1500 MHz),the shielding efficiency of rare earth magnesium alloy decreases at 380℃ to 420℃,which is attributed to the decrease ofthe conductivity of the alloy and the decrease of the reflection and absorption loss of the alloy;The electromagnetic shielding performance of the alloy increases when the temperature of upsetting is 460℃ to 500℃,which is attributed to the increase of grain boundary surface area that caused by the dynamic recrystallization when upsetting at a higher temperature,thus the propagation path and the consumption of electromagnetic wave in the alloy are increased.By comparing the mechanical properties and shielding performance of the upsetting alloy under different deformation temperatures,it is concluded that 460℃ is the best deformation temperature to improve its strength and electromagnetic shielding performance simultaneously.(2)Direct aging treatment(T5)can improve the shielding performance of the rare earth magnesium alloy.The reason that a large number of ageing precipitated phases leads to the decrease of the solute concentration and the increase of the electrical conductivity of the alloy,thus strengthening the consumption of the alloy on the electromagnetic wave.Moreover,the precipitated phase particles increase the interphase boundary surface area of the alloy,which can increase the reflection probability of electromagnetic wave and increase consumption.It is worth noting that too long aging time will lead to coarsening of grain and second phase,which will weaken the strengthening effect of electromagnetic shielding performance in aging process.(3)The electromagnetic shielding performance of the rare earth magnesium alloy can be divided into two stages in the process of solid solution aging(T6): In the stage of solid solution,the grain growth causes the decrease of multiple reflection and absorption loss,the increase of the solute concentration leads to the decrease of conductivity,the decrease of reflection loss and the decrease of shielding efficiency of alloy;At the aging stage,the precipitation of the second phase increases the electrical conductivity of the alloy,and the second phase particle can increase the interphase boundary surface area and strengthen the electromagnetic shielding performance of the alloy.(4)The effect of direct aging and solution aging on the shielding performance of the rare earth magnesium alloy was comprehensively compared.It was found that the comprehensive properties of the rare earth magnesium alloy subjected to direct aging were better than that of solid solution aged alloy.The heat treatment method with the highest mechanical properties is direct aging(225℃×24h),and the best heat treatment method with electromagnetic shielding efficiency is direct aging(225℃×72h). |
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