Study On Preparation And Properties Of Conductive Thermal Control Coatings On 6061 Aluminum Alloy

Aluminum alloy has occupied the focus on the aerospace materials due to its low density and quite good mechanical properties.But because of the severe space environment,surface material of spacecraft must have good thermal control performance and electrical conductivity property together,so it is in urgent need to investigate high-performance conductive thermal control coating on the aluminum alloy.In this dissertation,the AZO/Al₂O₃-ZnO conductive thermal control coating was prepared on6061 aluminum alloy in-situ by the method of micro-arc oxidation（MAO）combined with magnetron sputtering.The morphology,elemental composition and distribution,phase composition,thickness and roughness of the coating were characterized.The Thermal control performance and electrical conductivity of the coating were tested,and the influencing factors of structure and properties were discussed.During the micro-arc oxidation process,the optimization of electrolyte composition was performed by orthogonal test.The experimental results showed that the optimal electrolyte composition was 30 g/L Na₅P₃O₁₀,20 g/L Na₂SiO₃ and 6 g/L KOH.Then,the influence of current density and power frequency on the structure and performance of the coating was studied.When the current density was 10 A/dm² and the power frequency was 500 Hz,the thermal control performance of the coating was optimized,and the emissivity was 0.844.In order to further improve the thermal control performance of the coating,Zn（H₂PO₄）₂ was selected as the additive to fabricate the porous Al₂O₃-ZnO thermal control coating.The results show that the addition of Zn²⁺optimized the morphology,element composition,crystal structure and surface condition of the coating.And the thermal control performance was improved,emissivity reached 0.881 while absorption reached 0.371,and theα_s/εwas 0.42.Aluminum-doped zinc oxide（AZO）thin film was deposited on the surface of Al₂O₃-ZnO coating by magnetron sputtering.AZO/Al₂O₃-ZnO conductive thermal control coating was successfully prepared.The characterization method studied the influence of sputtering pressure,sputtering power,sputtering temperature and sputtering time on the composition,structure and properties of the composite coating were studied by various characterization methods,such as SEM,EDS,XPS and XRD.The results showed that the tunable preparation of AZO/Al₂O₃-ZnO composite coating could be achieved by controlling magnetron sputtering process parameters.The absorption and emission ratio of the film could be adjusted within 0.40-0.70,and the surface sheet resistance could be adjusted within 1-10³Ω/sq.When the sputtering pressure was 0.4 Pa,the sputtering power was 300 W,the substrate temperature was 200°C and the sputtering time was 0.5 h,the thermal performance of the composite coating was optimal,the absorption-emission ratio was 0.40,and the sheet resistance reached 289.8Ω/sq,which met requirements of spacecraft.