Research On Mg-Zn-Y Alloy Structure And Electromagnetic Shielding Performance

With the development of science and technology,the electromagnetic radiation pollution is more and more serious,the development of electromagnetic shielding material is imperative.Existing research shows that,compared with the traditional metal,composite shielding material,magnesium alloy has the advantages of low density,light weight,good mechanical properties.Mg-Zn-Y alloy is a high-strength magnesium alloy which has good plasticity and corrosion resistance.However,the study for the Mg-Zn-Y alloy electromagnetic shielding performance is very limited.Especially,how the characteristics,arrangement of the LPSO phase in Mg-Zn-Y alloys influence the electromagnetic shielding properties has not been revealed.This article take the Mg-Zn-Y alloy as the research object.This paper systematically calculated the characteristics of the LPSO phase,including electronic structure,bonding characteristics,phase stability and mechanical properties,by using First principle.At the same time,how the characteristics and arrangement of LPSO influence the electromagnetic shielding performance were calculated.Then,the electromagnetic shielding model with LPSO phase magnesium alloy was designed.Afterwards,based on the model,the Mg_98.5Zn_0.5Y₁ alloy was prepared by directional solidification.The Mg_98.5Zn_0.5Y₁ alloy were studied by using OM,SEM,EBSD,TEM and XRD.Meanwhile,the electromagnetic shielding performance of Mg_98.5Zn_0.5Y₁ alloy was analyzed with the addition of Zr and asynchronous rolling.At the same time,the microstructure evolution and mechanical properties of the alloy under asynchronous rolling and equal channel extrusion were studied.The main results are following:Firstly,in order to gain a better understanding of the microstructure and properties of the14H-LPSO,W phase and provide a basis for analyzing the effect of second phase on the relative microstructure and electromagnetic shielding properties,the band structure,electronic structure and elastic properties of 14H-LPSO and W phase?Mg₃Y₂Zn₃?in Mg-Zn-Y alloy were calculated by CASTEP program based on density functional theory.The bonding of 14H-LPSO phase is mainly among the valence electrons of Mg 3s,Zn 4s,Y 4p and little Y 4d orbits.The bonding of W phase is mainly among the valence electrons of Mg 3s,Zn 3p,Y4d orbits.The analysis of the energy density showed that the two phases contain covalent bonds,the bond of the W phase was stronger and the structure was more stable.The result was consistent with the state density analysis.The conductive relationship was?-Mg>14H-LPSO>W.By calculating the elastic constants,the mechanical properties of W phase and 14H-LPSO were deduced,and the following properties can be predicted:?1?The plasticity of the three was?-Mg>14H-LPSO>W.?2?The W phase resistance to deformation was greater than 14H-LPSO phase.?3?The W phase and 14H-LPSO showed brittleness,Mg showed plasticity.Secondly,in order to establish a foundation for subsequent experiments,the influence of conductivity,permeability and arrangement of LPSO phase on the electromagnetic shielding performance was systematically calculated.The results showed that the transmission parameters of the electromagnetic wave decreased with the increase of the conductivity of the LPSO phase,and the reflection intensity of the electromagnetic wave was higher.When the LPSO phase permeability increased,the attenuation coefficient of the electromagnetic wave in the LPSO phase increased.Although the the degree of attenuation of electromagnetic waves increased,the LPSO relative to the electromagnetic wave reflectivity reduced at some extent.Compared to a single uniform planar body shielding model,the shielding performance of double-layer LPSO-?-Mg uniform shielding model were better than single plane shield by calculating the equivalent transmission line shielding theory.The reflective loss increased twice,while absorption loss and multiple reflection loss have increased to some extent.On this basis,the electromagnetic shielding model of LPSO phase homogeneously arranged in Mg-Zn-Y alloy was proposed.Thirdly,in order to get the electromagnetic shielding model with LPSO phase homogeneously arranged in Mg-Zn-Y alloy.The Mg_98.5Zn_0.5Y₁ alloy was prepared by directional solidification.The relationship between the LPSO phase and the matrix,the formation of LPSO phase,how the LPSO phase influence the electromagnetic shielding performance were anylaized.At the same time,the effect of the addition of Zr on the microstructure and electromagnetic shielding properties of the alloy was analyzed.The results showed that the growth direction of the alloy grains was roughly the same and the structure of the 14H-LPSO phase was directly formed in the alloy.The 14H-LPSO included ABCA and ACBA stacking structure which had mutual twin relationship.The formation of the 14H-LPSO phase was accompanied by the generation of the stacking fault,which is formed on the Mg matrix.The direction of extension was parallel to the[1210]of?-Mg.The orientation relationship between the layer fault and the matrix was the same as that of the slice 14H-LPSO phase and the matrix.The electromagnetic shielding performance of directional solidified Mg_98.5Zn_0.5Y₁ alloy is 71¹13dB.By comparing the electromagnetic shielding properties of ordinary cast and oriented solidified Mg_98.5Zn_0.5Y₁ alloy,it was found that the ordered LPSO phase can increase the electromagnetic shielding performance.When the Zr element was added to the alloy,the grain size decreased,the LPSO phase was refined,the area of the grain boundary increased.The addition of Zr can not only improve the mechanical properties of the alloy,but also enhance the electromagnetic shielding of the material in the high frequency.Fourthly,in order to further control the orientation of LPSO phase,the effect of asynchronous rolling on the microstructure and electromagnetic shielding properties of Mg_98.5Zn_0.5Y₁ alloy was investigated.The results of the asynchronous rolling of the Mg_98.5Zn_0.5Y₁ alloy showed that the large amount of twins were produced in the alloy due to the large shearing force caused by the asynchronous rolling process.The?0002?<1010>base texture was formed.The 14H-LPSO has a certain inhibitory effect on the recrystallization of the alloy.With the increase of rolling temperature,and deformation,the plasticity of the alloy improved.With the increase of rolling times,the degree of LPSO phase deflection gradually increased,in the four times to the time,gradually approaching the direction of RD.With the increase of the rolling temperature,the non-basal slip system starts,the yield strength and tensile strength of the alloy decrease,while the elongation increases rapidly.The increase of the rolling reduction contributes to the yield strength and tensile strength of the alloy.After rolling the conductivity of the alloy was declined,the electromagnetic shielding performance increased by about 20dB.The electromagnetic shielding performance of alloy after rolling is 88¹12dB.There were two reason,one is that,the arrangement of the LPSO phase in the grains was more uniform and compact,increasing the absorption loss and multiple reflection losses,the other is,in the rolling process of the formation of the base texture,the conductivity of the different nature of the rolling surface and air impedance does not match the degree of a significant increase,resulting in reflection loss?SE_R?was significantly improved.The electromagnetic shielding of the alloy also improved to a certain extent.At last,the microstructures and properties of directional solidification Mg_98.5Zn_0.5Y₁ alloy under equal channel extrusion were investigated,and the change rule of LPSO phase in the process of equal channel extrusion was discussed.The results showed that the grains of the alloy were obviously refined.The base texture was formed.A large number of lamellar 14H-LPSO can exacerbate grain refinement.In the process of equal channel extrusion,14H-LPSO phase deformation had experienced from deformation,kink staggered,to fracture three stages.The yield strength and ultimate compressive strength of the alloy reached 240Mpa and 295Mpa,respectively,and the elongation decreased gradually with the increase of the number of times.After the equal channel extrusion,the conductivity of the Mg_98.5Zn_0.5Y₁ alloy gradually decreased.This was attributed to the increase in grain boundaries and lattice distortion.