| The rapid development of electronic technology has facilitated our life,but also brought electromagnetic interference and pollution problems.The development of electromagnetic shielding materials,as the basis for achieving electromagnetic shielding,becomes particularly important.Magnesium alloy has the advantages of light weight and high specific strength,and also displays good thermal conductivity and electromagnetic shielding properties.In the context of the increasing requirements for the integration of the functional structure of materials,it can be expected that magnesium alloys with the advantage of light weight and good mechanical properties and electromagnetic shielding properties will have more space for use.In this paper,Mg-6Zn-3Sn-xCu(x=0,0.5,1.0,1.5 wt.%)alloys(referred to as ZT63xCu alloys)were investigated using OM,SEM,TEM,EBSD and other material research methods as well as room temperature tensile properties test and micro-coaxial electromagnetic shielding properties test.The as-cast structure ZT63-xCu alloys and their homogenization behavior,hot compression deformation behavior,as well as the structure,mechanical properties and electromagnetic shielding properties of the alloys after extrusion deformation and aging treatment were specifically investigated.The strengthening mechanism and electromagnetic shielding mechanism of the alloys were revealed.The study of the as-cast ZT63-xCu alloys shows that the phase composition of the ZT63 alloy is ?-Mg,Mg2Zn3 phase and Mg2Sn phase,and the MgZnCu phase is formed in the alloy after the introduction of Cu element.The content of the MgZnCu phase gradually increases with the increase of Cu content.The increase in the brittle MgZnCu phase leads to a decrease in the mechanical properties of the alloys.The homogenization behavior of ZT63-xCu alloys shows that the two-stage homogenization treatment can make the ZT63-xCu alloys obtain a good homogenization effect.The homogenization system of ZT63 alloy is 335?/24 h+400?/6 h,and the homogenization system of Cu-containing alloy is 335?/24 h+420?/24 h.The high melting point MgZnCu phase cannot be completely decomposed during homogenization and the volume fraction of the residual MgZnCu phase increases with the increase of Cu content.The study of the hot compression behavior of the alloy shows that dynamic recrystallization occurs during plastic deformation.The hot compression deformation behavior of the alloy is influenced by the combination of deformation temperature,strain rate and degree of deformation.The increase in deformation temperature,the decrease in strain rate and the increase in the degree of deformation are conducive to the dynamic recrystallization of the alloy.The dynamic recrystallization mechanisms during hot compression are mainly discontinuous dynamic recrystallization,particle stimulation nucleation(PSN)recrystallization and continuous dynamic recrystallization.The thermal processing diagram shows that good processing results can be obtained for the alloy in the processing interval of deformation temperature 370-380? and strain rate close to 1 s-1.All the ZT63-xCu alloys undergo complete dynamic recrystallization after extrusion deformation,and the spherical Mg2Sn phase precipitates.The basal fiber texture,i.e.,(0001)Mg//ED direction,is formed in the extruded ZT63-xCu alloys,where the 0.5Cu alloy has the largest texture intensity.The combined effects of fine-grain strengthening,solid solution strengthening,texture strengthening and precipitation strengthening make the extruded ZT63-xCu alloys have good mechanical properties.The 0.5Cu alloy has the best mechanical properties with a tensile strength of 319 MPa and an elongation of 13%.The mechanical properties of the alloy decrease when Cu elements are added in excessive amounts.The shielding effectiveness of the alloy is greater than 90 dB in the range of 301500 MHz,which has good electromagnetic shielding performance.The presence of fiber texture makes the electromagnetic shielding performance of the extruded alloy anisotropic,and the cross-section along the extrusion direction has better electromagnetic shielding performance.In addition,the grain boundary of the alloy also affects the electromagnetic shielding performance of the alloy,but its effect is relatively small.The peak aging precipitated phase of ZT63-xCu alloys is mainly a short rod-shaped?'1 phase,which is oriented along with the[0001]Mg in the long-axis direction,and the phase interface is coherent with the matrix.At the same time,there is a small amount of ?'2 phase in the peak-aged alloy,which is distributed on the(0001)Mg basal plane in a disk shape.The size of both ?'1 and ?'2 phases increases significantly after the aging time is extended,with the ?'1 phase transforming into a slender rod,and the ?'2 phase expanding on the(0001)Mg plane.The 0.5Cu alloy has the best mechanical properties after singlestage aging treatment at 180?,with the corresponding peak aging system of 180?/6 h.The tensile strength of the alloy is 366 MPa and the elongation is 7%.The improved mechanical properties of the alloy after aging treatment are attributed to the strengthening effect of the ?'1 phase.During the double-stage aging treatment,the alloy forms a large number of G.P zones in the pre-aging stage,which provide the conditions for the formation of dense precipitation phases.As a result,the mechanical properties of the ZT63-xCu alloys are significantly improved.In particular,the 0.5Cu alloy still has the best mechanical properties with the best aging system of 90?/24 h+165?/8 h.The tensile strength of the alloy is 380 MPa and the elongation is 4%.The mechanical properties of the alloy are not greatly improved by the solid solution and aging treatment.The reason is that the increase of grain size in the solid solution stage adversely affects the mechanical properties of the alloy.The ZT63-xCu alloys in the peak-aged state exhibited good electromagnetic shielding properties after the double-stage aging treatment.The good electromagnetic properties come from the increase of its conductivity and the formation of internal multiple reflection interfaces.The electromagnetic shielding performance of the 0.5Cu alloy is 104-109 dB in the range of 30-1500 MHz.Collectively,the 0.5Cu alloy has the best mechanical properties matched with the electromagnetic shielding performance. |
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