镁锂合金是目前最轻的金属结构材料，因具有优良的比强度、导电导热性及电磁屏蔽性等众多优异特性，在国防工业、航天航空、生物医药等诸多领域应用前景广阔。然而，镁锂合金活泼的化学性质、极差的耐腐蚀能力，严重制约了其发展和广泛应用。如何有效提升镁锂合金的耐蚀性，是当前亟需解决的瓶颈问题。本文先采用蒸汽法在LA43M镁锂合金表面制备了蒸汽膜(SC)；随后采用水热法，分别调控水热温度、水热时间及溶液成分在优化后的SC表面制备了层状双金属氢氧化物膜层(Layered Doubled Hydroxides, LDH)，即LDH/SC复合膜层。使用扫描电镜（SEM）、X射线衍射仪（XRD）、红外光谱分析仪（FI-IR）检测了各膜层的微观组织、物相及成分。并借助析氢实验、浸泡实验及摩擦磨损实验分别表征了不同参数下SC、LDH/SC复合膜层的耐蚀性能、摩擦磨损性能。旨在系统性探究上述参数对LDH/SC复合膜层的生长特性、微观结构、耐蚀性能、摩擦磨损性能的影响，并阐明了复合膜层形成机理和耐蚀机理。

     本文主要研究内容及结论如下：

  （1）采用原位蒸汽法在LA43M基体表面制备了SC，并研究了蒸汽温度和蒸汽时间对SC耐蚀性能的影响。结果显示该膜主要由Mg(OH)₂、MgO两相组成。不同蒸汽处理所制备的SC耐蚀性大小顺序分别为：SC_{120 ℃} > SC_{130 ℃} > SC_{110 ℃} > LA43M基体；SC_{9 h} > SC_{6 h} > SC_{3 h} > SC_{12 h} > LA43M基体。表明SC能一定程度增强基体的耐蚀性能且120 ℃、9 h制备的SC耐蚀效果较好。

  （2）为进一步增强SC的耐蚀性能，以单一Al(NO₃)₃溶液作为水热溶液在优化的SC表面制备了Mg-Al LDH复合膜层，并探究了水热温度及水热时间对Mg-Al LDH复合膜层微观结构和耐蚀性能的影响。结果表明，Mg-Al LDH复合膜层可起到良好的密封效果。随着水热温度的升高，SC中的微孔被封闭，且膜层中LDH纳米片的数量增多，尺寸增大，厚度也逐渐增加。当水热温度为100 ℃时，复合膜层的致密度和厚度均达到最佳，在腐蚀溶液中具有最小的析氢速率和失重速率，并显示出优异的耐蚀性。适当延长水热时间可以促进LDH纳米片的形核及生长，且在水热时间为30 h时获得了均匀致密，且耐蚀性能优异的复合膜层，该膜层能在腐蚀溶液中稳定存在，且对基体起到长久有效的保护。

   （3）为构建多元化的复合膜层防腐体系，以Al(NO₃)₃和Co(NO₃)₃混合溶液为水热溶液在SC表面制备了Mg-Al-Co LDH三元复合膜层。研究发现，Mg-Al-Co LDH复合膜层也能使SC的致密度及耐蚀性得到提升，但因表面LDH纳米片尺寸和数量较Mg-Al LDH复合膜层均降低，长期耐蚀效果较差。

  （4）探究了基体及各膜层的摩擦学性能。结果表明，基体的平均摩擦系数最大（0.552），磨损程度最为严重，磨痕深且宽（约768 μm），磨损机制为严重的磨粒磨损及氧化磨损。而LDH/SC复合膜层试样摩擦系数均小于单一的SC和LA43M合金基体，且摩擦磨损性能显著改善。其中，Mg-Al LDH/SC复合膜层摩擦学性能良好，磨损机理为轻微磨粒磨损、黏着磨损。

   （5）探究了LDH/SC复合膜层的形成机理和耐蚀机理。结果表明，在水热反应过程中，SC中部分MgO、Mg(OH)₂溶解形成Mg²⁺；另一方面，水热溶液也与基体接触，使之局部溶解形成Mg²⁺进入溶液，两者在碱性条件下相继形成Mg(OH)₂、LDH纳米片，并逐渐密封了SC中微孔和裂纹等缺陷，最终生成了致密且完整的LDH/SC复合膜。LDH/SC复合膜层具有长期耐蚀性能的原因可归结于LDH/SC复合膜层的物理阻隔作用、独特的离子可交换性和稳定的化学性质及自修复作用。

    由此可见，在LA43M镁锂合金表面制备LDH/SC复合膜层后，不仅能显著增强其耐蚀性能，而且也能对摩擦磨损性能起到一定的改善作用，这将对镁锂合金的广泛应用提供参考。

   Magnesium-lithium (Mg-Li) alloys are the lightest metal structural materials. It has broad application prospects in many fields such as national defense industry, aerospace and biomedicine, due to its excellent specific strength, electrical and thermal conductivity and electromagnetic shielding. However, the active chemical properties and poor corrosion resistance of Mg-Li alloys seriously restricts their further development and application. How to effectively improve the corrosion resistance of Mg-Li alloys is a bottleneck problem that needs to be solved urgently. In this paper, the SC film was first prepared on the LA43M Mg-Li alloy substrate by steam method. Subsequently, LDH/SC composite coatings were fabricated on the optimized SC surface by hydrothermal method by adjusting hydrothermal temperature, hydrothermal time and solution composition. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and infrared spectroscopy (FI-IR) were used to detect the microstructure, phase and composition of SC and LDH/SC composite coatings. The corrosion resistance and friction and wear properties of SC and LDH/SC composite coatings were characterized by hydrogen evolution test, immersion test and friction and wear test. The purpose was to systematically explore the above parameters on the growth behavior, microstructure, corrosion resistance, friction and wear properties of LDH/SC composite coating, and then to clarify the formation mechanism and corrosion resistance mechanism.

     The main research contents and conclusions of this paper are as follows:

     (1) SC was prepared on the surface of LA43M substrate by in-situ steam method, and the effects of steam temperature and steam time on the corrosion resistance of SC were investigated. The results show that the SC is mainly composed of Mg(OH)₂ and MgO phases. The order of corrosion resistance of SC prepared by different steam treatment is: SC_{120 °C} > SC_{130 °C} > SC_{110 °C} > LA43M substrate, SC_{9 h} > SC_{6 h} > SC_{3 h} > SC_{12 h} > LA43M substrate. The SC prepared at 120 °C for 9 h has the smallest hydrogen evolution rate (0.00753 mL·cm^-2·h^-1) and weight loss rate (0.00413 mg·cm^-2·h^-1), indicating that SC can enhance the corrosion resistance of the substrate to a certain extent and the SC prepared at 120 °C for 9 h has better corrosion resistance.

      (2) In order to further enhance the corrosion resistance of SC, a single Al(NO₃)₃ solution was used to prepare Mg-Al LDH composite coating on the basis of the optimized SC. The effects of hydrothermal temperature and hydrothermal time on the microstructure and properties of the Mg-Al LDH composite coating were investigated. The results show that the Mg-Al LDH composite coating can play a good sealing effect. With the increase of hydrothermal temperature, the number of LDH nanosheets increases, the size gradually increases, the thickness gradually increases, and the density first increases and then decreases. When the hydrothermal temperature is 100 °C, the composite coating has the best density and thickness, the smallest hydrogen evolution rate and weight loss rate in the corrosion solution, which exhibited the excellent corrosion resistance. The appropriate extension of hydrothermal time is beneficial to the nucleation and growth of LDH nanosheets and the improvement of corrosion resistance. The composite coating with dense structure and excellent corrosion resistance was obtained when the hydrothermal time was 30 h, which can effectively protect the substrate for a long time.

      (3) In order to construct a diversified anti-corrosion system of composite coating, Mg-Al-Co LDH ternary composite coating was prepared on the surface of SC by using Al(NO₃)₃ and Co(NO₃)₃ mixed solution as hydrothermal solution. It was found that the Mg-Al-Co LDH composite coating also improve the density and corrosion resistance of SC, but the long-term corrosion resistance was poor because the size and number of LDH nanosheets on the surface were lower than those of Mg-Al LDH composite coating.

       (4) The tribological properties of the substrate and the coatings were also investigated. The friction and wear results show that the average friction coefficient of the substrate is the largest (0.552), and the wear degree is the most serious. The wear scar is deep and wide (768 μm), and the wear mechanism is severe abrasive wear and oxidative wear. The friction coefficient of the prepared LDH/SC composite coating samples is smaller than that of the single SC and LA43M substrate, and the friction and wear properties are significantly improved. Among them, the Mg-Al LDH/SC composite coating has good tribological properties, and the wear mechanism is slight abrasive wear and adhesive wear.

    (5) The formation mechanism and corrosion resistance mechanism of LDH/SC composite coating were studied. The results show that during the hydrothermal reaction, some MgO and Mg(OH)₂ in SC dissolved to form Mg²⁺, on the other hand, Mg in the substrate dissolves locally to form Mg²⁺. Subsequently, under alkaline conditions, the Mg(OH)₂ and LDH nanosheets were formed one after another, gradually sealing defects such as micropores and cracks in SC, and finally forming a dense and complete LDH/SC composite coating. The reason for the long-term corrosion resistance of LDH/SC composite coating can be attributed to the physical barrier effect, unique ion exchange, stable chemical properties and self-healing effect of LDH/SC composite coating.

     It can be seen that the preparation of LDH/SC composite coating on the surface of LA43M magnesium-lithium alloy can not only significantly enhance its corrosion resistance, but also improve its tribological properties, which will provide reference for the wide application of magnesium-lithium alloy.