Preparation And Optical Properties Of Ni-Cu Nano-porous Membrane On AZ91D Magnesium Alloy By Dealloying In Ionic Liquid

In recent years,China's aerospace industry has developed vigorously,providing a broad development platform for magnesium alloys.In the field of aerospace,magnesium alloys are often used in the manufacture of electronic product shells.Because aerospace electronic products must run normally in the space environment for a long time,they require good electromagnetic shield and high heat-sinking capability.However,the existing technologies cannot meet the requirements of high conductivity and high infrared emissivity.In this study,AZ91D magnesium alloy was used as substrate,and Ni-Cu nanoporous membrane was prepared by dealloying from choline chloride-urea ionic liquid.The Ni-Cu nanoporous coating has high conductivity and high infrared emissivity.After a series of pretreatment(Ni P electroless-plating or Cu electroplating),Ni-Cu/Cu-Ni multilayers were electroplated on the surface of AZ91D magnesium alloy in ionic liquid.The research shows that in the process of electrodeposition,Cu²⁺deposites on prior to Ni²⁺.With the increase of current density,the atomic concentration of Ni in the Ni-Cu membrane increases significantly and then tends to be smooth.The thickness of Ni-Cu membrane is about 1?1.5?m per layer.On this basis,Ni-Cu nanoporous membrane was prepared by dealloying method.The effects of dealloying potential and dealloying current density on the structure and properties of Ni-Cu nanoporous membranes were mainly studied.When dealloying under constant current,the main element that removed from membrane is Ni.When the continuous network microstructure is basically formed,the Ni and Cu are uniformly removed from the Ni-Cu/Cu-Ni multilayer.The evolution process of the microstructure is as follows:when dealloying begins,ball cluster and bubble-shape microstructure appears on the surface of the membrane.Then the ball continuously sinks into the hole,and cone-shape protuberance appears on the top of the bubble-shape microstructure.Finally,the cone-shape protuberance develops into continuous network microstructure.With the increase of the dealloying current density,the average emissivity of the sample increases first and then decreases.With the increase of the dealloying time,the average emissivity of the sample increases first,and then rises again.The best parameters of constant-current dealloying are as follows:I=2.83 m A/cm²,t=1200s.The resistivity of Ni-Cu nanoporous membrane is less than0.00025?·m,and the infrared emissivity is 0.63.When dealloying under constant potential,Ni is removed from Ni-Cu/Cu-Ni multilayer in the beginning.Then Cu is removed from Ni-Cu/Cu-Ni multilayer.Then Cu is removed from electroplating Cu intermediate layer.Finally,AZ91D magnesium alloy is directly corroded.The evolution process of the microstructure is as follows:First,the continuous network microstructure is formed.Then the thickness of the network microstructure and the width of the pore are gradually increased.With the increase of the dealloying time,the average emissivity of the sample increases first and then decreases.The best parameters of constant-potential dealloying are as follows:?=-0.1 V,t=5400s.The resistivity of Ni-Cu nanoporous membrane is less than 0.00025?·m,and the infrared emissivity is 0.62.The structure of Ni-Cu/Cu-Ni multilayer significantly improves the emissivity of the Ni-Cu nanoporous membrane in the NIR and MIR.The number of layers can be further increased,to improve the infrared emissivity.