微弧氧化后Mg-8Li合金表面MgLiAlY-LDHs@GO膜层的生长及耐蚀性能

目的 提高Mg-8Li合金的耐蚀性能。方法 首先在Mg-8Li合金表面制备微弧氧化膜(MAO)，然后使用原位水热法在微弧氧化膜表面原位生长掺杂氧化石墨烯(GO)的四元(MgLiAlY)层状双羟基金属氧化物(LDHs)智能自修复膜层。采用SEM、XRD、FT-IR、EDS、ICP等手段研究MgLiAlY-LDHs@GO膜层的形貌、结构以及成分。通过EIS、Tafel以及浸泡试验等研究膜层的耐蚀性能，分析膜层的腐蚀行为，阐释其耐蚀机理。结果 GO的掺杂可以促使LDHs纳米片生长得更加致密，主体层板中具有缓蚀作用的Y³⁺可以提高涂层的耐蚀性，四元LDHs的生长所需要的Mg²⁺、Li⁺、Al³⁺等离子来源于镁锂合金基体以及微弧氧化膜的溶解，其中Li⁺也可以促进LDHs纳米片生长得更为均匀细密。膜层的腐蚀电流密度为6.03×10^–7 A/cm²，比MAO膜层降低了1个数量级，提高了镁锂合金的耐蚀性能。结论 GO的负载使LDHs的耐蚀性能和膜层稳定性均有一定程度的提升，引入稀土元素Y会改变LDHs的骨架，造成晶格畸变，使得LDHs微观形貌呈现褶皱状，剩下部分以Y(OH)3形式存在于涂层表面，可进一步提高膜层的耐蚀性能和稳定性。

Growth Behavior and Corrosion Resistance of MgLiAlY-LDHs@GO on Mg-8Li Alloy after Micro Arc Oxidation

Magnesium-lithium alloy is currently the world''s lightest metal structural material, with high specific strength, high specific stiffness, good seismic performance and many other advantages, and has a good prospect in aerospace, digital communications, new energy and other fields. However, the electrode potential of magnesium-lithium alloys is low, resulting in poor corrosion resistance, so its application development has been seriously affected. Currently, the enhancement of the corrosion resistance of magnesium and lithium alloys can be divided into two methods:heat treatment and deformation processing through the alloy from the alloy alloying, or the magnesium and lithium alloys prepared on the surface of the protective coating. These methods can only play a passive corrosion-resistant effect because the damage may be caused immediately or the failure may be formed gradually. Self-healing coatings are now gradually attracting attention, compared with the above methods and it can realize the effect of active corrosion resistance, so the self-healing coatings to LDHs coating become more prominent. The micro arc oxidation (MAO) was carried out on the surface of Mg-8Li alloy at first, and then a quaternary (MgLiAlY) layered double hydroxides (LDHs) smart self-repairing coating doped with graphene oxide (GO) was grown on the surface after the micro arc oxidation in-situ by hydrothermal method. The morphology, structure, and composition of the MgLiAlY@GO coating were investigated by SEM, XRD, FT-IR, EDS, and ICP. The corrosion resistance of the coating was investigated by EIS, Tafel and immersion tests. The corrosion behavior of the coating was analyzed and the corrosion resistance mechanism was elucidated. The doping of GO could promote the growth of LDHs nanosheets to become denser. Y3+, which had a corrosion inhibiting effect on the main layer plate, could improve the corrosion resistance of the coating. The Mg2+, Li+, and Al3+ required for the growth of quaternary LDHs came from the dissolution of magnesium lithium alloy matrix and micro arc oxidation coatings. Li+ could also promote the growth of LDHs nanosheets to be more uniform. The corrosion current density of the coating was 6.03×10–7 A/cm2, which was one order of magnitude lower than the MAO coating, improving the corrosion resistance of magnesium lithium alloy. Compared with binary LDHs, poly-LDHs could relatively adsorb more anions in order to maintain the equilibrium charge of the interlayer channel, which endowed poly-LDHs with the ability to capture more corrosion anions and further improve the corrosion resistance of the LDHs coating. The surface of GO was rich in negative charge, which had good theoretical suitability with positively charged LDHs, providing more nucleation sites for the growth of LDHs nanosheets, changing the way of LDHs nanosheets growing perpendicularly to the substrate, and solving the problem of porosity of traditional LDHs coating. The GO doping will give the coating a "labyrinth effect", so that the obtained membrane coating has a certain degree of improvement in corrosion resistance and stability. The introduction of the Y changes the skeleton of LDHs and causes lattice distortion, which results in the micro-morphology of LDHs showing a folded appearance, and the remaining part exists on the surface of the coating in the form of Y(OH)3, which can impart self-healing properties to the coating.