Achieving Excellent Electromagnetic Interference Shielding Effectiveness in High Rare Earth Mg-12Gd-3Y alloy via Nd Addition Combined with Hot Rolling and Aging

Achieving excellent electromagnetic interference(EMI)shielding effectiveness(SE)in high rare earth(RE)-content Mg alloys is currently a significant technical challenge.This work systematically investigated the effects of different Nd elements on the electrical conductivity and EMI SE of Mg-12Gd-3Y-xNd alloy by adding Nd elements to the high RE content Mg-12Gd-3Y alloy,followed by a combined process of hot rolling and aging(R-A).The results indicate that the addition of Nd elements leads to reduced solid solubility of Gd and Y,resulting in a large amount of precipitation.The Mg-12Gd-3Y-2.0Nd alloy has the optimum EMI SE after 63%R-A treatment,reaching 88-118 dB at 30-1500 MHz.The Mg-12Gd-3Y-xNd alloy has acicular and granular forms of the Mg5(Gd,Y,Nd)(abbreviated as Mg5RE)phase after R-A treatment.The granular Mg5RE phase gradually breaks up and refines into more minor scales with increasing rolling reduction and is diffusely distributed in the matrix.The acicular Mg5RE phase is densely arranged,with cross-distribution in some areas.The cross-distributed acicular Mg5RE phase,the delicate granular Mg5RE phase,and the denseβ′phase provide more interfaces for reflecting electromagnetic waves and increase the multiple reflection loss of incident electromagnetic waves.In addition,the Mg-12Gd-3Y-xNd alloy deflects most of the c-axis of the grains parallel to the normal direction(ND)as the rolling reduction increases,making the impedance difference between the plate surface and air larger.The increased impedance makes the material reflect more loss to incident electromagnetic waves.The combined use of these two leads to an excellent EMI SE of Mg-12Gd-3Y-xNd with high RE content after R-A treatment.

Dielectric,Electromagnetic Interference Shielding and Absorption Properties of Si_3N_4-PyC Composite Ceramics

Pyrolytic carbon （PyC） was infiltrated into silicon nitride （Si3N4） ceramics by precursor infiltration and pyrolysis （PIP） of phenolic resin, and Ni nanoparticles were added into the phenolic resin to change the electric conductivity of Si3N4-PyC composite ceramics. Dielectric permittivity, electromagnetic interference （EMI） shielding and absorption properties of Si3N4-PyC composite ceramics were studied as a function of Ni content at 8.2-12.4 GHz （X-band）. When Ni nanoparticles were added into phenolic resin, the electric conductivity of the prepared composite ceramics decreased with increasing Ni content, which was attributed to the decrease of graphitization degree of PyC. The decrease in electric conductivity led to the decrease in both permittivity and EMI shielding effectiveness. Since too high permittivity is harmful to the impendence match and results in the strong reflection, the electromagnetic wave absorption property of Si3N4-PyC composite ceramics increases with increasing Ni content. When the content of Ni nanoparticles added into phenolic resin was 2 wt%, the composite ceramics possessed the lowest electric conductivity and displayed the most excellent absorption property with a minimum reflection loss as low as -28.9 dB.