Effect Of Coloring Salt On Thermal Control And Anti-corrosion Properties Of PEO Coatings On LA103Z Magnesium-lithium Alloy

Magnesium-lithium alloys are called"ultra-light alloys",and the application of Mg-Li alloys in aerospace can directly reduce the fuel combustion and transportation costs of spacecraft.Therefore,we used plasma electrolytic oxidation(PEO)technology to prepare black ceramic coatings with high absorption and high emission on the surface of LA103Z Mg-Li alloys.Because the anti-corrosion property of Mg-Li alloys is poor,this work will improve its anti-corrosion property.The main work is as follows:(1)The PEO coatings were prepared using silicate as electrolyte and CuSO₄as additive.The PEO coatings are mainly composed of MgO and Mg₂Si O₄phases.With the increase of CuSO₄concentration,electrical parameters and reaction time,the diffraction peak intensity of MgO increases,while that of Mg-Li alloy matrix decreases.The surface of the coatings is typical porous.With the increase of CuSO₄concentration and the prolongation of reaction time,the color of the coatings gradually changed from silver-gray to reddish-brown,and then to dark black.The roughness and thickness of the coatings showed an upward trend,and the absorptivity and emissivity of the coatings are consistent with their variation laws.The PEO coatings are mainly composed of Mg,O,Si,Na,and Cu,and the content of Cu increases with the increase of CuSO₄concentration.XPS results show that Cu mainly exists in the coatings in the form of monovalent and divalent cupric ions.Combining XRD and XPS results,it can be inferred that amorphous copper oxide and cuprous oxide are the main color components of the coatings.When the concentration of CuSO₄is 1.25g/L and the reaction time is 20min,the absorptivity and emissivity are as high as 0.8150 and 0.9072.(2)The thermal control coatings prepared with NH₄VO₃as colorant mainly consists of MgO phase.The coatings are mainly composed of O,Mg,P,Na,Si,V and other elements,and the content of V element increases with the increase of NH₄VO₃concentration.XPS results show that the main chromogenic components of the coatings are VO₂,V₂O₃and V₂O₅.Prolonging the reaction time and increasing the concentration of NH₄VO₃can improve the thickness,roughness,absorptivity and emissivity of the coatings.When the current density is too high(6.26A/dm~2),the surface appearance of the coatings changes greatly,which is detrimental to its thermal control performance.When the concentration of NH₄VO₃is 10g/L,the absorptivity and emissivity of the coatings are 0.9408 and 0.9315.The coating has better thermal control prooerty than adding copper salt.In addition,the coatings have good adhesion and thermal stability.The surface morphology,absorptivity and emissivity of the coatings have no significant difference before and after high temperature treatment.After 25 thermal shock treatment,the coatings begin to fall off from the edge.(3)The anti-corrosion property of the coated samples added with different coloring salts were investigated by electrochemical tests.The results show that the PEO coatings have a corrosion potential(E_corr)higher than that of the substrate during the corrosion process.The PEO coatings protect the substrate.Properly increasing the concentration of coloring salt and reaction parameters is beneficial to the corrosion resistance of the coatings.When the copper salt concentration was 1.25g/L,the corrosion current(I_corr)of the coating decreased by two orders of magnitude to 4.130×10^-7A cm~2,and the polarization resistance(R_P)was as high as76152?·cm~2.When the concentration of vanadium salt is 10g/L,the I_corrof the coating is1.805×10^-7A cm~2,and the R_Pvalue is 450 times that of the substrate.The coating exhibits better corrosion resistance than the addition of copper salts.