In this study, a vanadium (V) and tannic acid-based composite conversion coating (VTACC) was prepared on 6063 aluminum alloy (AA6063) to increase its corrosion resistance. The surface morphology and compositions of the VTACCs were characterized using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS). The corrosion resistance of the coatings was investigated by linear polarization and electrochemical impedance spectra (EIS). The self-healing ability of the coating was detected by SEM, EDS, and scanning vibrating electrode technique (SVET) measurements. The coating mainly consisted of metal oxides, including Al2O3, VO2, V2O3, and V2O5, and metal organic complexes (Al and V-complexes). The electrochemical measurement results indicated that the best corrosion resistance of VTACC was acquired when the treatment time was 12 min. Furthermore, because a new coating with vanadium rich oxide was developed on the scratch area, artificial scratch VTACC surfaces were repaired after several days of immersion in 3.5-wt% NaCl solution.

In this work, ZnLaAl layered double hydroxides (LDHs) were prepared by the co-precipitation method, and the ZnLaAl-LDHs nanosheets were embedded in sol-gel coating for the corrosion protection of 6061 aluminum alloys. The structure, morphology, and long-term anti-corrosion performance of sol-gel coating modified with ZnLaAl-LDHs were investigated. The structure and morphology analysis showed that nanosheets of ZnLaAl-LDHs are finer than those of ZnAl-LDHs, with the results suggesting that the La can refine the size of LDHs’ nanosheets and improve their nucleation rate. The results of long-term corrosion tests showed that the sol-gel coating with ZnLaAl-LDHs exhibits higher corrosion resistance and better stability compared with the sol-gel coating with ZnAl-LDHs, which indicates that the addition of La enhances the anti-corrosion performance of the LDHs and improves the stability of sol-gel coating with LDHs. Finally, the formation mechanism of ZnLaAl-LDHs and the corrosion mechanism of sol-gel coating with ZnLaAl-LDHs on 6061 aluminum alloys are both discussed in detail.

通过对传统锆/钛基转化膜成膜机理的分析，提出了提升锆/钛基转化膜性能的设计理念，并分别在5083铝合金和AZ91D镁合金上进行了实践，显著提升了合金基体的耐腐蚀性能及其与有机涂层的附着性能。通过解析影响锆/钛基转化膜性能的关键因素，指出了当前锆/钛基转化膜研究的不足及其未来的发展方向。

采用响应曲面法对微弧氧化电解液体系进行了优化，并在5083铝合金表面进行了单致密微弧氧化涂层的制备。通过扫描电镜、X射线衍射仪、显微硬度计和极化曲线对铝合金微弧氧化膜的微观组织、显微硬度和耐蚀性进行了研究。结果表明：随着微弧氧化膜层厚度从30 μm增加到90 μm，烧结颗粒的尺寸从约为10 μm增加到约为50 μm，致密层由最初的20 μm增加到70 μm，陶瓷膜层中α-Al₂O₃的比例明显增加，涂层的硬度由900 HV提高到1500 HV。依据极化曲线和盐雾实验结果发现：随着微弧氧化时间的增加，微弧氧化膜的自腐蚀电流密度逐渐降低，钝化能力逐渐增强，膜层的耐腐蚀性能大幅度提高。

The fast leaching and robust barrier property of inhibitors are the basic fundamentals for the formation of active protective coatings to protect aluminum alloys. Herein, an active protective surface was developed based on an epoxy coating and an underlying lithium carbonate (Li2CO3)-treated anodized aluminum alloy 2024-T3. The morphology of the Li-LDH layer was studied to know its formation mechanism. The electrochemical studies revealed that the fast and adequate leaching of lithium led to a substantial increment of corrosion resistance of the scratched coating in 3.5 wt% NaCl from 1 to 8 days. Time of flight secondary ion mass spectroscopy (ToF-SIMS) results indicated that Li was distributed in the lateral direction and covered the scratched area. The 3D images indicated that different lithium compounds were formed and 90% of the scratched area was covered with the lithium protective layer over immersion time. A combined approach of morphology observations, electrochemical measurements, and ToF-SIMS showed the lithium protective layer offered good corrosion resistance. On the contrary, lithium provided fast and adequate leaching from the coating, demonstrating good active protection for aluminum and its alloys.

Aluminum alloys are known to have many advantages (e.g., light weight and low cost) but they are not immune to corrosion. So, it is important to assess their corrosion behavior, in particular under atmospheric conditions. To protect aluminum alloys against corrosion, paints are generally applied onto the materials. Corrosion protection in the aerospace industry consists of a conversion or anodized coating, an inhibited primer, and a top-coat. Chromate conversion coating (CCC) and primers containing chromate pigments have been widely used in the aerospace industry over the last decades. However, new environmental regulations have led to major changes for aluminum corrosion protection. By limiting or prohibiting some chemicals, for instance Cr(VI), the European regulation REACH (Regulation on Registration Evaluation, Authorization and Restriction of Chemicals) has induced major changes to some of the finishing processes of aluminum alloys (e.g., chromate conversion, chromic acid anodizing, and chromate sealing). Interesting results have been obtained while seeking replacements for Cr(VI), for example, with the incorporation of cerium, lithium salt, or nanocontainers loaded with corrosion inhibitors in organic coatings. For several years, hybrid sol–gel coatings able to replace the pre-treatment and primer steps have been under development, showing interesting results. New prospects for the future involve the use of photopolymerization to reduce the energy-intensive heat treatment needed in sol–gel technology. It will also be necessary to test these new technologies in service conditions or in accelerated corrosion tests before being able to conclude on the real effectiveness of these coatings. This review summarizes the recent developments in Cr-free coatings for aluminum alloys. Their advantages and drawbacks are also discussed.

Corrosion of metallic components represents a major issue in the aeronautical sector, giving rise to safety concerns and significant financial damages. Conversion coatings (CC) based on hexavalent chromium provide exceptional corrosion protection at relatively low cost. However, environmental issues and health concerns raised a growing interest in the development of alternative technologies. These must not only be cost effective and environmentally friendly but also provide corrosion resistance and adhesion performance comparable to Cr6+-based CCs. Simultaneously fulfilling all of these criteria is a difficult challenge, and an industrial application has so far only been achieved by a small number of systems. This review critically summarizes the recent scientific literature and patents for chromate-free CCs on aluminum alloys and tries to assess their potential regarding the highly demanding aerospace requirements. The bath composition and coating characteristics of the trivalent chromium process, rare earth chemical conversion coatings, transition metal oxyanion additives, Zr/Ti-based chemical conversion coatings, sol-gel coatings, and smart coatings providing stimulus-related inhibitor release are discussed. The advantages and disadvantages of the alternative technologies with regard to their practical implementation are debated, as the aeronautics industry is confronted with the necessity to move away from chromates in the near term.

This paper aims to develop a chromium-free chemical conversion coating with good corrosion resistance. A novel chemical conversion coating was prepared on 6061 aluminum alloy by dipping in the treatment solution containing titanium/zirconium based-ions and sodium metaphosphate and cerium nitrate hexahydrate as additives. The morphology and composition of the conversion coatings were observed by scanning electron microscopy and energy dispersive X-ray spectroscopy. The microarea structure of conversion coatings at different formation stages was analyzed by electron probe microanalyzer. The electrochemical polarization curve revealed that the corrosion potential of the conversion coating was -0.577 V and the corrosion current density was 0.1148 mu A/cm(2). The equivalent circuit fitted by AC impedance showed that the film resistance reaches 68,140 omega. The formation of coating preferentially grows on the Al (Fe) Si intermetallic to form oxides of Ti and Zr; then TiO2 formed by a higher concentration of Ti4+ gradually covered ZrO2. Ce3+ could adsorb on the intermetallic compound, the hydrolysis of which causes the local pH of the solution to decrease and promotes the aluminum alloy dissolved.

采用多巴胺对氮化硼进行非共价改性，通过SEM、红外光谱和TGA对粉末进行了表征。使用浸泡法在40Cr合金钢表面制备了掺杂改性氮化硼 (mBN) 的硅烷复合膜，运用SEM、红外光谱、润湿性测试以及动电位极化曲线研究了硅烷复合膜的耐蚀性能。结果表明，聚多巴胺成功附着在氮化硼表面，掺杂mBN的硅烷膜厚度增大至1.812 μm，mBN/BTESPT硅烷复合膜的表面接触角达到91.97°，动电位腐蚀电流密度为9.187×10^-8 A/cm²，耐蚀性能相比单一硅烷膜提高了约30倍，在中性盐雾测试中表现出较好的耐蚀性。mBN通过对硅烷膜的物理填充与化学键结合，阻碍了腐蚀介质的扩散，显著增强了金属的耐蚀性能。

为了解决Cu合金在海水中的腐蚀问题,促进Cu合金部件在海洋工程装备和设施中的应用,采用电镀与磁控溅射相结合的方法,首先在Cu衬底上电镀Ni层,随后在Ni层上溅射沉积Ni-Cr合金薄膜,最后在Ni-Cr层上再溅射沉积不同Cr含量的Ni-Cr-Al-Si合金薄膜,获得Ni/Ni-Cr/Ni-Cr-Al-Si梯度复合膜层,并研究了该梯度复合膜层的结构与腐蚀性能。结果表明：在海水中,Cr含量为43.05%的梯度复合膜层 (S2样品),其低频端阻抗值、容抗弧半径、最大相位角、电荷转移电阻R_f和腐蚀电位最大,表明其耐腐蚀性能最好。在所研究的范围内,梯度膜层的Ni-Cr-Al-Si表层中[Al]/[Cr]原子比率越大,其耐腐蚀性越好。梯度复合膜层的腐蚀过程主要为点蚀,膜层表面团簇的界面处是点蚀的中心。适当Cr含量的Ni/Ni-Cr/Ni-Cr-Al-Si梯度复合膜层具有很好的耐海水腐蚀和导热能力,适合作为海水中使用的Cu换热器表面的防护涂层。

In this communication, a bis-silane prepolymer was used to modify epoxy resin, aiming to enhance the corrosion resistance of epoxy coatings on aluminum alloy substrates. The bis-silane prepolymer was prepared by tetraethoxysilane (TEOS) and γ-glycidoxypropyl trimethoxysilane (GPTMS). The corrosion behavior of silane-epoxy coatings was studied. Compared with silane monomer-modified epoxy coatings, bis-silane-modified epoxy coatings have lower coating capacitance (Cc), higher charge transfer resistances (Rdl), and lower double layer capacitance (Cdl) during long-time immersion. It indicates that bis-silane-modified epoxy coating has stronger waterproof permeability and substrate corrosion protection ability. In addition, due to the leaching of the silane component and cross-linking reaction between different silanes during the immersion process, the bis-silane-modified epoxy coatings exhibit much stronger “self-healing” ability.