Preparation And Thermal Control Performance Of Mao Caotings On Magnesium And Magnesium-lithium Alloy

As "Lightweight engineering metal structure material",Mg alloy can meet the requirements of weight loss in aerospace field.As the lightest structural material,MgLi alloy can better meet the lightweight and thermal protection requirements of space vehicles.The thermal control coating can adapt well to the thermal radiation environment in space and ensure the normal operation of the spacecraft internal equipment,which is of great value to the space field.This work uses micro-arc oxidation to prepare high absorption and high emissivity thermal control coatings on the surface of Mg and Mg-Li alloys.The phase composition,structure and morphology of the coatings are characterized by roughness meter,thickness meter,SEM?EDS?XRD and XPS.The absorption and emissivity are tested and the relationship between the thermal control properties of the coatings and the morphology,composition and structure were analyzed.By means of emission spectroscopy?OES?,the state of spark discharge in micro-arc oxidation process was analyzed,and the effect of spark discharge behavior on the morphology,structure and thermal control of the coating were studied.The thermal controlled coatings prepared on the surface of Mg alloy and Mg-Li alloy all have porous structure,which is mainly composed of amorphous phase materials of Si,V,O and other elements.Thermal control properties are related to coating thickness,roughness and black substance.Black color of the coating is mainly caused by the V₂O₃ in the coating.Increasing reaction time and electrolyte concentration,the morphology and structure of the coating surface changed,the thickness and roughness increased,the area of external radiation energy increased,the content of black matter increased,and the absorption and emissivity increased.The electrical parameters have little effect on the thermal control performance under the condition of electrolytic liquid system and reaction time.The thermal control coating has good thermal stability,the coating after high temperature treatment does not change color,and the absorption and emissivity are basically unchanged.The excellent performance of the thermal control coating can be well adapted to the high and low temperature alternating situation of spacecraft in orbit.Under the condition of 10 g/L NH₄VO₃ and 10 min of reaction time,the surface of Mg alloy and Mg-Li alloy has the most excellent thermal control performance.The highest absorption and emissivity of Mg alloy thermal control coating are 0.952 and 0.941,respectively.The high absorption and emissivity of Mg-Li alloy are 0.964,0.951.The micro-arc oxidation process mainly includes Na,Li and Mg element discharge,the discharge intensity of different discharge elements is different.Spectral calculation shows that the ion temperature?T_e? of spark discharge is about 5430 K,and the temperature change during the reaction can be roughly divided into two stages.The electron concentration?N_e? is about 2.271×10¹⁶ cm^-3.Characteristic changes of spark discharge,corresponding to different reaction stages of microarc oxidation.According to the spark discharge theory,the distribution,structure and growth process of the surface elements of the film were analyzed.The thickness,roughness and surface morphology of the coating during the discharge were summarized.The effect of plasma discharge on the thermal control properties of the coating was analyzed.It is found that when the spark discharge is mainly of the type of "internal-electrolyte interface discharge of the coating" and the type of strong discharge of the metal substrateelectrolyte-coating interface ",the coating has excellent structure and thermal control performance.