Preparation And Properties Of High Solar Absorption And High Emissivity Coatings On Aluminium Alloy

Aluminum alloys have been widely used for the spacecraft due to its attractive mechanical properties including higher specific strength(strength/density),durability and damage tolerance.Orbital spacecraft suffers the extreme temperature cycling owing to direct sun load on one side and deep cold space on the other,which reduces the component lifetime.As a result,effective thermal prevention measures are very necessary to ensure the normal operation of devices and instruments in the spacecraft.This work prepared the thermal control coatings with the properties of high absorptivity(?)and high emissivity(?s)by anodic oxidation(AAO).The thickness,roughness and microstructure of the coatings were measured.The relationship between thermal control properties and surface state was analyzed.(1)The effect of different process parameters(current density,oxidation temperature,oxidation time)on the surface properties,absorptivity and emissivity are studied.The optimized parameters are:current density 5A/dm²,oxidation temperature0?and the reaction time 60 min.A high absorptivity and high emissivity thermal control coating with an absorptivity of 0.921 and an emissivity of 0.96 was obtained.Prolong the reaction time,increase the current density,the pore size of the coating become lager,the thickness and roughness increased.Thus increase the absorptivity and emissivity.The lower the temperature,the greater the thickness and the greater the absorptivity.The relationship between thickness and absorptivity was studied.The thicker coating can block the absorption of energy by the substrate,thus increasing the absorptivity.(2)The effects of different electrolyte components(sulfuric acid concentration,oxalic acid concentration,iron sulfate)on the surface properties,absorptivity and emissivity are studied.The optimized parameters are:sulfuric acid 40 g/L,oxalic acid40 g/L,oxalic acid 6 g/L.Increasing the concentration of sulfuric acid,the pore size of the coating becomes larger,the thickness decreases and the roughness increases,which leads to the decrease of its absorptivity and the increase of emissivity.In addition,the addition of oxalic acid and iron sulfate significantly increased the roughness and thickness,changed the morphology,the absorptivity emissivity increased.Fe ions enter the coating in the form of Fe₃O₄ effectively improve the absorption and emissivity of the coating.(3)In order to further improve the spatial protection ability of the oxide film,KH-550 was used to silanize the surface of the aluminum alloy anodizing film.The effect of silane hydrolysis temperature on the micro-surface morphology and thermal properties of the film was studied.After silane sealing,the absorption of the film changed little and the emissivity became smaller.When the temperature of silane sealing hole is 50°C,the sealing effect is the best,and its corrosion resistance is the best.The relationship between roughness and emissivity was studied.The increase of the roughness increased its surface area,which can increase the area of external radiation energy of the coating,thus increasing the e missivity of the coating.The film through the silane sealing shows a certain hydrophobic performance.Through the delayed icing experiment,it is found that the film can effectively delay the icing time of the surface,and its anti-icing performance has been greatly improved.