Study On Electromagnetic Shielding Properties Of Mg_98.5Zn_0.5Y Alloy By Asynchronous Rollin

With the rapid development of 5G communication,electric vehicles and electronic devices,conventional copper,nickel and other electromagnetic shielding materials due to its high cost,high density,environmental pollution and other problems can no longer fully meet the increasing frequency of electromagnetic radiation,the spectrum is increasingly expanding protection needs,so the development and innovation of new functional shielding materials can not wait.Magnesium and magnesium alloys,as the lightest metal structure material,not only have good damping performance,processing performance and biocompatibility,but also show excellent full-spectrum electromagnetic shielding performance.The Mg-Zn-Y alloy is a high-strength magnesium alloy with a long periodically ordered phase（LPSO）as the reinforcing phase and an internal multi-reflective medium,which can effectively improve the mechanical properties and electromagnetic shielding performance of the alloy,making it a prime choice for new lightweight and high-performance electromagnetic shielding materials.In this paper,Mg_98.5Zn_0.5Y ingots containingα-Mg/14H-LPSO lamellar structure were prepared by gravity casting process,and the morphology and dislocation charac teristics ofα-Mg/14H-LPSO lamellar structure were investigated by OM,SEM and TEM testing methods.The lamellar structure and orientation were regulated by asynchronous rolling to explore the influence of the lamellar structure on the electromagnetic shie lding properties and mechanical properties of Mg_98.5Zn_0.5Y alloy before and after the evolution of the lamellar structure.The results of the study are as follows.（1）Anα-Mg/14H-LPSO lamellar structure Mg_{9 8.5}Zn_0.5Y alloy containing a high number density was prepared by gravity casting.The lamellar structure is distributed throughout the grains and parallel to the inner grains,with a flat and smooth phase interface and clearly visible contours.The lamellar structures in the different grains are at certain angles due to the different grain orientations.（2）Asynchronous rolling facilitates the subsequent plastic deformation of the structurally anisotropicα-Mg/14H-LPSO lamellar structure.During thermal deformation,the as-cast Mg_98.5Zn_0.5Y alloy deforms from slip and twinning to grain boundary slip and grain rotation due to the narrow spacing of the high number densityα-Mg/14H-LPSO lamellar structure（down to 9.6μm）,which hinders dislocation slip and twinning formation.Therefore,with t he increase of deformation,the structural orientation ofα-Mg/14H-LPSO lamellar gradually deflects along with the grain in the direction of rolling RD,and after three passes of deformation,the structural orientation ofα-Mg/14H-LPSO lamellar tends to be unified.During the rolling process,theα-Mg/14H-LPSO lamellar structure shape changed from parallel to twisted,the 14H-LPSO phase elongated and thinned under the action of asynchronous rolling shear,and the 14H-LPSO phase newly precipitated in theα-Mg matrix,resulting in a significant increase in the number ofα-Mg/14H-LPSO lamellar structures.（3）During the rolling process,the parallel and smooth interface ofα-Mg/14H-LPSO lamellae became rough due to the back stress inhomogeneity of the lamellar structure.After three passes of rolling,the interface ofα-Mg/14H-LPSO lamellar became blurred from clear to blurred,and the radius of curvature of particles at theα-Mg/14H-LPSO lamellar thickened and"cratered"reached the maximum.（4）With the increase of rolling passes,the thickness of Mg _98.5Zn_0.5Y alloy sheet gradually thinned to 0.75mm（three passes）,and the corresponding conductivity value gradually decreased.The electromagnetic shielding performance of the alloy shows an increasing trend in th e case of lower thickness and lower conductivity,and the electromagnetic shielding effectiveness of the thin Mg alloy sheet with thickness of0.75 mm is up to 100 d B～105 d B in the frequency band of 30～1500 MHz.This is mainly related to the reduction of t he sheet layer spacing,the increase of the number density and the rough sheet layer interface.（5）The tensile strength of the as-cast Mg_98.5Zn_0.5Y alloy was 89 MPa,and the tensile strength of Mg_98.5Zn_0.5Y alloys after one and two passes of asynchronous rolling deformation are 162 MPa and 165 MPa,respectively,compared with the initial state of magnesium alloy strength increased by about 82%and 85%.The tensile strength of the Mg_98.5Zn_0.5Y alloy after three passes of rolling increased again to 185MPa,which was about 108%higher compared to the as-cast alloy.It was found that the nanoscale high number density multilayerα-Mg/14H-LPSO lamellar structure plays a decisive role in influencing the mechanical properties of Mg _98.5Zn_0.5Y alloy,where the number density of 14H-LPSO phase,the size of lamellar spacing and stacking fault are the main factors affecting the mechanical properties of the magnesium alloy.Therefore,the yield strength（σ）of the Mg_{9 8.5}Zn_0.5Y alloy can be predicted to be related to the lamellar spacing strengthening mechanism（σ_L）,stacking fault strengthening mechanism（σ_p）,and the"fiber strengthening mechanism"（σ_F）.