| Due to the special requirements of heat dissipation and electromagnetic shielding of aerospace products,a kind of surface treatment technology which is suitable for magnesium lithium alloy with high infrared emissivity and high conductivity is needed.The porous nickel coating with high emissivity and high conductivity was prepared by hydrogen bubble template method.The effect of different deposition time,ammonium chloride and nickel chloride concentration on the porous coating aperture,hole projection area and the infrared emissivity of coating were studied.The relationship between the emissivity of the coating and the projection area of the coating was analyzed.Furthermore,the infrared radiation properties of the composite coatings were studied.The results show that the porous coating can effectively improve the infrared emissivity of the coating and maintain the high conductivity of the alloy coating.The porous Zn-Ni alloy coatings were electrodeposited by alloying method,and the effects of Zn content on the pore size,pore area ratio,infrared emissivity and conductivity were investigated.The results show that the addition of Zn can obviously increase the pore size of porous coating and make the coating more loose,which can obviously improve the infrared emissivity of porous coating and the coating with high conductivity.However,the addition of Zn can greatly reduce the adhesion between the coating and the substrate,and the coating is loose and easy to fall off.In this paper,the adhesion between the coating and the substrate and the physical properties of the coating were improved by adding NH4SCN.The addition of NH4SCN can effectively coordinate with metal ions to form[Ni(SCN)4]2-and[Zn(SCN)4]2-complex,which can effectively improve the reduction potential of metal ions.The results show that the addition of NH4SCN can not only improve the bonding force between the coating and the substrate,but also keep the high conductivity of the porous coating.Based on the study of the infrared emissivity of porous coatings,the optimum parameters of porous alloy coatings with high infrared emissivity and high conductivity were prepared on the surface of Mg Li alloy.The pretreatment process of Mg Li alloy:Degrease?Acid pickling?Prepassivation?Electroless Ni-P?Plating Cu coating.The middle composite coating can effectively improve the corrosion resistance of Mg Li alloy,and the copper layer can effectively improve the bonding force with the subsequent porous coating.The results show that the infrared emissivity of the porous Zn-Ni coating prepared on the surface of Mg Li alloy is 0.90,and the resistivity is less than 0.01 m?·cm,which has a high conductivity.The results show that the coating has good adhesion with the substrate and the coating.Through this study,on the surface of magnesium lithium alloy was prepared with high infrared emissivity and conductivity of the coating,the outermost layer of porous Zn-Ni alloy coating is mainly composed of Ni2Zn11,Ni O and Ni S,the infrared emission rate is 0.90,the resistivity is less than 0.01 m?·cm. |
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