镁合金表面防腐蚀超疏水涂层制备研究进展

镁合金是一种有发展前途的绿色工程金属材料,但其较差的抗腐蚀性能限制了它的大规模应用。对镁合金表面进行超疏水处理,能够极大地提高镁合金的耐腐蚀性能。当超疏水试样浸泡在腐蚀溶液中时,该结构将在腐蚀介质中形成固-气-液界面层,减少镁合金表面与腐蚀介质之间的接触面积,从而降低腐蚀速度。超疏水表面需要满足微纳米结构和低表面能2个必要条件。可以采用二步法或一步法在镁合金表面制备超疏水表面,详细介绍了在镁合金表面构造微纳米结构的方法,包括激光处理、机加工、化学刻蚀、化学镀、电化学沉积、阳极氧化、微弧氧化、水热合成和喷涂等方法。超疏水表面一旦受到机械损伤,微纳米结构无法满足条件,超疏水表面的“气垫效应”消失,腐蚀介质就会直接与微纳米结构接触,因此需要保证构建的微纳米粗糙结构对镁基体具有良好的保护作用并具有自愈功能。通过制备复合涂层,提高下层微纳米结构的自愈合性能,上层涂层的超疏水性与下层涂层的良好物理屏障能力的协同效应可以改善涂层的长久耐腐蚀性能。综述了在镁合金上制备具有良好耐腐蚀性能的复合超疏水表面的方法,并对镁合金超疏水表面防护技术的研究方向进行了展望。

Research Progress in the Preparation of Anti-corrosion Superhydrophobic Coatings on Magnesium Alloys

Magnesium alloy is a promising green engineering metal material, but its poor corrosion resistance limits its large-scale application. The corrosion resistance and service life of magnesium alloy can be improved by surface treatment. The surface protection technology of magnesium alloy includes electrochemical method (micro-arc oxidation, electrodeposition), chemical conversion method and organic coating protection method. Superhydrophobic surfaces have great application prospects in daily life, industry and agriculture because of their self-cleaning, oil-water separation, anti-icing and anti-corrosion properties. Superhydrophobic treatment of magnesium alloy surface can greatly improve the corrosion resistance of magnesium alloy. Superhydrophobic surfaces refer to surfaces with a contact angle greater than 150° and a sliding angle less than 10°. When the superhydrophobic sample is immersed in the corrosive solution, the structure will form a solid-gas-liquid interface layer in the corrosive medium, reducing the contact area between the magnesium alloy surface and the corrosive medium, thereby reducing the corrosion rate. The superhydrophobic surface needs to meet the two necessary conditions of micro and nano structure and low surface energy. Superhydrophobic surface can be prepared on the surface of magnesium alloy by two-step method or one-step method. The two-step method for preparing superhydrophobic surface of magnesium alloy generally means that micro and nano structures are constructed on the alloy surface first, and then low surface energy modification is carried out. One step method means that both roughness and low surface energy can be achieved simultaneously on the surface of magnesium alloy. This paper describes in detail the methods of constructing micro and nano structures on the surface of magnesium alloy, including laser treatment, machining, chemical etching, electroless plating, electrochemical deposition, anodic oxidation, micro-arc oxidation, hydrothermal synthesis and spraying. Low surface energy materials for preparing superhydrophobic surfaces include long-chain fatty carboxylic acid, fluorosilane, Long chain alkyl silanes, polydimethylsiloxanes and polypropylene (PP), etc. Common carboxylic acids include stearic acid (SA), myristate acid (MA), lauric acid (dodecanoic acid, LA), octadecylphosphonic acid, perfluorocaprylic acid, oleic acid, etc. Fluorosilane include 1H,1H,2H,2H-Perfluorodecyltriethoxysilane (FAS), 1H,1H,2H,2H-Perfluorodecyltrimethoxysilane (PFDTMS), 1H,1H,2H,2H-Perfluorooctyltriethoxysilane(PFOTES), Hexadecyltrimethoxysilane (HDTMS) , etc. However, when the superhydrophobic surface is used for anti-corrosion, once the superhydrophobic surface is damaged, the "air cushion effect" of the superhydrophobic surface will disappear, and the corrosive medium will directly contact the micro and nano structure. Therefore, in this case, it is also necessary to ensure that the constructed micro and nano rough structure has a good protection effect on the magnesium matrix. To this end, it is necessary to develop composite coatings to improve the self-healing properties of the micro and nano structures and the corrosion resistance of the coating under the superhydrophobic surface. The synergistic effect between the superhydrophobicity of the upper coating and the good physical barrier ability of the lower coating can improve the long-term corrosion resistance of the coating. Due to the layered structure of LDH, the synergistic effect of superhydrophobic effect and chloride ion exchange performance can improve the corrosion resistance of the coating, so there are more superhydrophobic composite coatings prepared together with LDH coatings. It has been studied that the combination of micro-arc oxidation coating (PEO) and layered double hydroxide (LDH) can not only seal the micropore defects on the PEO film, but also enable the composite film to have self-healing function when loaded with corrosion inhibitors. Furthermore, surface superhydrophobic modification can greatly improve the long-term corrosion resistance of the composite coating. In this paper, the anticorrosive mechanism of superhydrophobic surface is introduced, and the method of preparing superhydrophobic surface with good corrosion resistance on magnesium alloy is reviewed. The research direction of superhydrophobic surface protection technology for magnesium alloys is also prospected.