镁锂合金是最轻的金属结构材料，由于其比强度高、弹性模量低、降噪减震性能和电磁屏蔽性能优越，被广泛应用于汽车，航空航天，3C电子，以及军工装备等诸多领域，然而镁锂合金电负性低，容易腐蚀，进一步应用和发展受到极大限制。目前，提高镁合金的耐蚀性最经济有效的方法为薄膜和涂层技术。层状双金属氢氧化物（layered double hydroxide，LDH）是一种由八面体结构相互共边形成的层状结构材料，其层间阴离子可交换性使其在防腐领域表现出巨大潜力。本研究即以LA103Z高锂含量镁锂合金为基体，通过调整水热反应时间、温度、溶液浓度、溶液种类诸参数，使用一步水热法于其表面原位生成LDH膜层。采用扫描电子显微镜（SEM）、能谱仪（EDS）、X射线衍射仪（XRD）、傅里叶变换红外光谱仪（FT-IR）检测膜层的表面、截面形貌和物相结构，并借助电化学阻抗谱（EIS）、动电位极化曲线和析氢实验对不同参数膜层的耐蚀性进行表征，旨在探究上述参数对LDH膜层的微观结构和耐蚀性的影响，揭示成膜机理和耐蚀机理，并优化出制备耐蚀性能优越的LDH膜层的工艺参数。

结果显示，使用原位水热法可以在LA103Z镁合金表面制得LDH膜层，该膜层含有LDH和Mg(OH)₂两相，其中LDH的主体层板由Mg、Al、（Co）、O八面体结构构成，插层离子为NO₃^-。LDH呈片状生长于膜层外侧，大部分纳米片趋向垂直生长于膜层表面低凹处，少数沿膜层凸起部位平行生长。

随水热时间延长，膜层表面的LDH尺寸变大，数量变多，膜厚随之增加，水热时间为24 h时，Mg-Al LDH膜层厚且致密，表面的LDH纳米片均匀紧凑，将表面基本覆盖，该膜层表现出最佳的耐蚀性能。当水热时间提升至30 h时，膜厚进一步增加，但表面的LDH纳米片尺寸减小，膜层内部出现空隙，耐蚀性能下降。可见，适当延长水热时间可促进LDH的形核与长大，提高膜层的耐蚀性，保温时间超过24 h，LDH膜层开始溶解，膜层耐蚀性反而下降。随水热温度的升高，纳米片的尺寸、数量以及对表面的覆盖程度均逐渐提升，此外，膜层厚度，主体膜层中的LDH含量也呈增加的趋势。高温LDH膜层（100、110 ℃）中存在许多空隙，长期耐腐蚀性能劣于90 ℃下的膜层。可见，适当提高水热反应温度可促进主体膜层中LDH含量的增加和LDH纳米片在膜层外表面的生长，从而提升Mg-Al LDH膜层的耐蚀性，但过高的水热温度（超过90 ℃）亦会降低其长期耐腐蚀性能。水热溶液中Al³⁺浓度影响LDH的生成量及膜基结合能力，Al(NO₃)₃溶液浓度较低（0.01 M），会使膜层主体层中无法生成LDH，膜层表面LDH纳米片少且细小；溶液浓度较高（0.09 M）则会使膜层和基体分离，膜厚减小。只有溶液浓度适当（0.05 M），才能得到厚且致密，表面LDH尺寸较大，耐蚀性能优异的LDH膜层。使用Al(NO₃)₃/Co(NO₃)₂混合溶液制得的Mg-Al-Co LDH膜层，其表面纳米片尺寸和数量相对于Mg-Al LDH膜层均降低，耐蚀性略有减小。

LDH膜层形成机理：LA103Z基体中的Mg溶解进入溶液，并在碱性环境下生成Mg(OH)₂前驱体，溶液中的Al³⁺（Co²⁺）替换Mg(OH)₂中Mg²⁺的位置，NO₃^-插入前驱体板层，形成LDH片状结构。随后，Mg(OH)₂和LDH纳米片相继生成，并最终铺满基体表面。但反应时间过长，高温水热溶液将透过表层的LDH，渗入Mg(OH)₂/LDH主体膜层内部，形成内部空隙。LDH膜层对基体的保护作用主要归结于两个方面：物理屏障作用，LDH的离子交换作用。

Magnesium-lithium (Mg-Li) alloy is the lightest metal structural material. It is widely used in many fields such as automobiles, aerospace, 3C electronics, and military equipment, due to its high specific strength, low elastic modulus, excellent noise reduction and shock absorption performance and electromagnetic shielding performance. However, the low electronegativity and corrosion resistance lor='red'>of Mg-Li alloy greatly limits its further application and development. At present, the most economical and effective methods to improve the corrosion resistance lor='red'>of magnesium alloys are thin film and coating technology. Layered double hydroxide (LDH) is a kind lor='red'>of layered material formed by octahedral structures, and its interlayer anion exchangeability makes it show great potential in the anti-corrosion field. In this study, LA103Z Mg-Li alloy with high lithium content was used as the substrate. Different LDH films were prepared in situ on its surface by one-step hydrothermal method via adjusting the parameters lor='red'>of hydrothermal reaction time, temperature, solution concentration and solution type. The surface, cross-section morphologies and phase compositions lor='red'>of films were detected by scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), and X-ray diffraction (XRD) and fourier transform infrared spectrometer (FT-IR), respectively. The corrosion resistance was characterized by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curve and hydrogen evolution test. The purpose was to explore the influence lor='red'>of the above parameters on microstructure and corrosion resistance lor='red'>of the LDH film, reveal the film formation mechanism and corrosion resistance mechanism, and optimize the process parameters for the preparation lor='red'>of LDH film with excellent corrosion resistance.

The results show that LDH films can be prepared on the surface lor='red'>of LA103Z Mg alloy by in-situ hydrothermal method, which contains two phases LDH and Mg(OH)₂. The main laminate lor='red'>of LDH is composed lor='red'>of octahedral structure including Mg, Al, (Co) and O, and the interlayer anion is NO₃^-. The LDH grows on the outer surface lor='red'>of the film in a flake shape, and most nano-sheets tend to grow vertically in the recessed areas, while a few grow parallel along the raised areas.

With the extension lor='red'>of hydrothermal time, the size and quantity lor='red'>of LDH nanosheets increased, and the film was thickened. After 24 h lor='red'>of hydrothermal treatment, the LDH nanosheets with uniform and compact distribution covered the film surface basically, and the LDH film was thick and dense, which exhibited the best corrosion resistance. When the hydrothermal time rised to 30 h, the thickness lor='red'>of the film further increased, but the corrosion resistance was poor owing to the fine nanosheet size and loose film structure. Therefore, an appropriate extension lor='red'>of the hydrothermal time can promote the nucleation and growth lor='red'>of LDH and improve the corrosion resistance lor='red'>of the film. When the hydrothermal time exceed 24 h, the LDH begins to dissolve, and the corrosion resistance lor='red'>of the film decreases. With the increase lor='red'>of hydrothermal temperature, the size, number and coverage lor='red'>of nano-sheets on the surface gradually increased. In addition, the film thickness and the LDH content in the main film also showed an increasing trend. There were many interspaces in tbe LDH films obtained at high hydrothermal temperatures (100 ℃, 110 ℃), and the long-term corrosion resistance was worse than that lor='red'>of the film at 90 ℃. It can be seen that proper increase lor='red'>of the hydrothermal temperature can increase the content lor='red'>of LDH in the main film and promote the growth lor='red'>of LDH nanosheets on the outer surface lor='red'>of the film, thus improving the corrosion resistance lor='red'>of the LDH film, but too high hydrothermal temperature (over 90 ℃) will reduce the long-term corrosion resistance. The concentration lor='red'>of Al³⁺ in hydrothermal solution affects the formation lor='red'>of LDH and the binding capacity between the film and substrate. Improper concentration lor='red'>of Al(NO₃)₃ (0.01 M) will prevent the formation lor='red'>of the LDH in the main film, and the surface LDH nano-sheets are few and fine. Too high solution concentration (0.09 M) will lead to the separation lor='red'>of the film from the substrate, and the film thickness will be reduced. Only in proper solution concentration (0.05 M), the thick and dense LDH film with large LDH size and excellent corrosion resistance can be obtained. Compared with the Mg-Al LDH film, the size and quantity lor='red'>of nanosheets on the surface lor='red'>of the Mg-Al-Co LDH film obtained in Al(NO₃)₃/Co(NO₃)₂ mixed solution decrease, and its corrosion resistance is slightly reduced.

Mechanism lor='red'>of LDH film formation: The Mg in the LA103Z substrate dissolves into the solution, and the Mg(OH)₂ precursor is formed in the alkaline environment. Al³⁺ (Co²⁺) in the solution replaces Mg²⁺ in Mg(OH)₂, and NO₃^- is inserted into the precursor plates, initially forming Mg-Al LDH flake structures. Subsequently, Mg(OH)₂ and LDH nanosheets are successively formed, and finally covers the substrate surface. However, after a long period lor='red'>of hydrothermal reaction, the high temperature hydrothermal solution will penetrate the LDH on the film surface and infiltrate into the interior lor='red'>of the Mg(OH)₂/LDH main film, forming interspaces. The protective effect lor='red'>of LDH film on the substrate can be mainly attributed to two aspects: the physical barrier effect and interlayer anion exchange lor='red'>of LDH.