Preparation And Properties Of LDH/MAO Composite Film On LA103Z Magnesium-Lithium Alloy

As a revolutionary material of "green and environmental protection" in the future,LA103Z magnesium-lithium alloy has been successfully applied to the support and part of the chassis of high orbit satellites.However,the LA103Z magnesium-lithium alloy contains about 10%lithium content,which leads to its high electrochemical activity and very negative electrode potential.Magnesium-lithium alloy is very susceptible to corrosion in a corrosive environment,which severely limits its extensive application.In this paper,the micro-arc oxidation(MAO)film was first prepared on LA103Z magnesium-lithium alloy,the Mg-Al LDH and the Mg-Al-Co layered double hydroxide(LDH)films were fabricated on MAO film by an in-situ hydrothermal method.The microscopic morphology and composition of the LDH/MAO composite film were systematically investigated.Meanwhile,the corrosion behavior of LDH/MAO in 3.5wt%NaCl solution was studied by hydrogen evolution method and weight loss method.A reciprocating wear tester was used to test the friction and wear properties of the composite film.In addition,the corrosion resistance mechanism of magnesium-lithium alloy LDH/MAO composite film was discussed.The MAO ceramic layer was prepared on the surface of LA103Z magnesium-lithium alloy by micro-arc oxidation technology.The results show that the MAO ceramic layer is mainly composed of MgO and Mg2SiO4 phases.The Hydrogen evolution volumes of MAOceramic layers prepared with different oxidation voltages after 192h immersion are ranked as follows:V450V<V500V<V550V<Vsubstrate.In addition,the MAO ceramic layer with an oxidation voltage of 500V has the minimum weight loss rate after immersing for 96h.It is demonstrated that the MAO ceramic layer can provide corrosion resistance protection for the substrate and the MAO ceramic layer prepared at 500V had the best anticorrosion capacity.In order to further improve its corrosion resistance,a Mg-Al LDH film was prepared on MAO film by a hydrothermal method to seal it.The results show that with the extension of the hydrothermal time and hydrothermal temperature,the spacing of the LDH nanosheets gradually decreases,the film is dense,and the micropores and microcracks on MAO film are successfully sealed.The corrosion resistance of the LDH/MAO composite film is much better than that of the LA103Z magnesium-lithium alloy.When the hydrothermal temperature parameter is 90? and the hydrothermal time parameter ranges from 18h to 24h,the LDH/MAO composite film has the minimum Hydrogen evolution volume and the weight loss rate.It shows that the LDH film can effectively seal the micropores of the MAO film and has longer corrosion resistance than the MAO film alone.In order to explore the sealing effect of different hydrothermal solutions,a Mg-Al-Co layered double hydroxide was prepared on MAO film by changing the parameters of LDH hydrothermal solution while keeping MAO process parameters unchanged.The results show that MgO on the surface of the MAO ceramic coating was partially dissolved during the hydrothermal treatment,and the released Mg2+ ions combined with OH-ions in the hydrothermal solution to form Mg(OH)2 nano-sheets,which were deposited on the surface of MAO film and its pores.The LDH nanosheets prepared by hydrothermal treatment for 24 hours have a dense structure and the best sealing effect.The immersion experiment shows that the Hydrogen evolution volume and weight loss rate of the LDH/MAO composite film are the lowest when the hydrothermal temperature parameter is 90? and the hydrothermal time parameter is 24h.The corrosion resistance of the LDH/MAO composite film layer is better than that of the MAO film layer alone and the LA103Z magnesium-lithium alloy.The wear morphology of LDH/MAO composite film shows that the surface of the composite film is bright and clean with less wear debris,only slight wear occurs on the surface of LDH/MAO film and there are scratches in different depths on LDH/MAO composite film.The friction coefficient of the samples sealed by the LDH/MAO composite film layer is lower than that of the MAO film layer alone and the LA103Z substrate,the friction and wear resistance is significantly improved.The long-term corrosion resistance mechanism of the LDH/MAO composite film can be summarized as:a combination of the barrier effect of the LDH coating,the ion-exchange property,self-healing and the synergistic protection effect of the LDH/MAO composite film.