Preparation And Corrosion Resistance Of Silane-Modified Micro-arc Oxidation Composite Film On Magnesium-Lithium Alloy Surface

There are micropores and microcracks in the micro-arc oxidation（MAO）coating on the surface of Mg-Li alloy,these defects limit the corrosion resistance of the micro-arc oxide coating.In this work,the micro-arc oxidation and silanization process were combined to prepare the double-layer microarc oxidation/3-glycidoxypropyltrimethoxysilane（KH560）composite coating on the surface of the LA103Z Mg-Li alloy.On this basis,the effects of reduced graphene oxide（RGO）modified KH560 film,8-hydroxyquinoline（8-HQ）pretreated MAO film and 8-HQ modified KH560 film on MAO/KH560 to the corrosion resistance of the composite film were investigated.The microstructure and composition of the film were characterized by SEM,EDS,XRD and FTIR.At the same time,the potentiodynamic polarization curve and EIS test were used to characterize the corrosion resistance of the composite film,and a salt spray tester was used to study the corrosion resistance of the samples in a neutral salt spray environment.The specific results are as follows:（1）In the experiment,a two-step method was used to prepare the MAO film and the RGO modified KH560 film on the surface of the Mg-Li alloy in turn.The experimental results show that the preparation of KH560 film and RGO-modified KH560 film on the surface of MAO film by silanization can effectively seal the micropores and microcracks of the MAO film on the surface of Mg-Li alloy inhibiting the corrosive medium contact with the Mg-Li alloy matrix.At the same time,the experimental results show that the RGO modification significantly improves the anti-corrosion performance of the KH560 film.The RGO modification significantly increases the film thickness of KH560 and the sealing effect.At the same time,the RGO nanosheets change the corrosion path from vertical to horizontal,extending the diffusion path of the corrosive medium,thereby inhibiting the contact between the corrosive medium such as H₂O and Cl^-and the substrate,which greatly improves the corrosion resistance of the MAO/KH560 composite film.（2）In the experiment,the MAO sample was soaked and pretreated in an alkaline solution of 8-HQ,so that a layer of MgQ₂ film was grown in situ on the surface of the MAO film.The layer is composed of micron-scale petal-like clusters,which fill the micropores of the MAO film to a certain extent;At the same time,due to the increase of surface hydroxyl groups and the increase of surface roughness,the adsorption of the hydrolyzed KH560 molecules by the MAO film layer is significantly improved.After the MAO film layer is silanized,the film thickness of the KH560 film layer is significantly thicker.Therefore,the 8-HQ pretreatment significantly enhanced the shielding effect of the MAO/MgQ₂/KH560 composite film on the corrosive medium.（3）The MAO/MgQ₂+KH560 composite film layer was prepared on the Mg-Li alloy MAO film by one-step method.By adding 8-HQ to the KH560hydrolyzate,the MAO samples underwent simultaneous silanization process and in-situ growth of MgQ₂ layers in the silane hydrolyzate.The MgQ₂ in the MAO/MgQ₂+KH560 composite film has a petal-like structure,which also promotes the thickening of the KH560 film,thereby enhancing the corrosion resistance of the composite film.