Study On Preparation And Properties Of Mg-Li Alloy With High Emissivity Coating

Mg-Li, the minimum density alloy of all currently, has been widely used inaviation, aerospace and military because of the high specific strength and specificstiffness. However, Mg-Li alloy with lower melting point （500℃）, has seriouslyhampered the application prospects. In this study, it improved the resistance of thesubstrate to temperature through the preparation of high emissivity composite coatings.To improve the shear strength between the composite coatings and the substrate, itprepared the micro-arc oxidation buffer layer which also enhanced the coatings’ thermalshock performance by reducing the coefficient of thermal expansion in all layers.During the preparation of transition layer，the subject exploreed the shear strengthbetween oxide coatings and substrate and the porosity of the oxide coatings which wereprepared in Na₂SiO₃, Na₃PO₄and NaAlO₂. Eventually, it adopted the mixed electrolyteswhich were composed by Na₃PO₄and NaAlO₂, and adjustd the concentration of eachgroup based on the shear strength. The experiment optimized the parameters of theconstant-current micro-arc oxidation equipment by orthogonal test. The parametersincluded duty cycle, pulse frequency and time. All parameters were selected based onshear strength and roughness. Finally, the shearing strength of films was18.85MPa andthe composite coatings’ was up to17.0MPa. The subject contrasted the coatings’performance which were prepared by diping, brushing and scrapering with Mn₂, andultimately to determine the superior coating under the scrapering process.The fillers of the coatings were the active ingredients for high emissivitycomposite coatings. This subject selected the raw materials of Mn₂, Fe₂O₃, CuO andCo₂O₃to synthesis composite powders based on the material composition, phasecomposition and crystal. It adopted solid phase synthesis method to prepared compositepowders and the sintering procedures were determined by TGA.The issue compared theemissivity of one-component, binary, ternary and quaternary compound powders. Theresults showed that the ternary of Mn-Co-Cu compounds had the highest emissivity at300℃. It was more than an average of0.8within the range of3-20μm bands.Composite powders were tetragonal spinel （Co,Mn）（Co,Mn）₂O₄mainly by XRD. Thatoctahedral vacancy was filled by Co²⁺and Mn³⁺by XPS and XRD analysis. Theelectrons transfering between the different monovalent ions increaseed the emissivity of3-6μm and the lattice vibration of spinel material determined the emissivity of the otherbands.The shear strength and emissivity properties of the coatings were the best underthe total thickness of38μm by scrapering in a specific curing process. The corrosioncurrent density of the coatings was lower than the substrate about two orders of magnitude.The emissivity of coatings increased with the increasing of thickness from32to42μm, but the shear strength reduced.