镁合金腐蚀研究进展(20)---Mg-1Li-1Ca表面MAO/SA超疏水涂层耐蚀性能

微弧氧化膜(micro-arc oxidation, MAO)是镁合金表面处理技术应用最为广泛的一类技术。但是，MAO涂层为多孔结构，且有许多微裂纹，对镁合金基体的保护较为有限。因此，为提高其长期耐蚀性，有必要对MAO涂层进行进一步封孔处理。

如果MAO表面封孔处理的同时赋予超疏水特性，那么 此MAO复合涂层的耐蚀性能将得到大幅提高。

超疏水表面一般是指与水的接触角大于150°、滚动角小于10°的表面。由于具有许多独特的表面性能，如自洁性、防污性、疏水性、耐蚀性等特点，超疏水表面已经广泛应用于金属材料表面改性。

自然界广泛存在超疏水表面。荷叶“出淤泥而不染，濯清涟而不妖”，描述了莲叶具有自清洁的特性。德国生物学家W.Barthlott和C.Neinhuisd对近300种植物叶表面进行深入研究，通过显微观察荷叶的微观结构，发现荷叶表面由许多乳突和一层蜡状物质组成，微米-纳米级的乳突和低表面能蜡状物质正是荷花自清洁性能的根本原因，从而解开了荷叶“出淤泥而不染”的神秘面纱[1-3]。因此，改变物质表面的粗糙度与表面形貌和通过具备低表面能物质对粗糙结构进行化学修饰是提高材料表面疏水性的重要途径[4-6].

低表面能物质硬脂酸(Stearic acid, SA)在多孔的MAO表面有良好的附着性能和疏水性能。当MAO涂层样品浸泡在硬脂酸溶液中，在高温环境下，硬脂酸通过MAO涂层的开孔结构与基体或MAO涂层发生反应，生成硬脂酸镁；硬脂酸镁为一种特殊的白色沉淀，存在于镁合金基体或MAO涂层表面。硬脂酸与涂层产生物理附着和化学反应，其疏水的烷基链接枝在MAO涂层表面。因而，MAO/SA复合涂层可以有效地阻挡介质与镁合金基体的直接接触，从而提高镁合金的耐蚀性能。

该工作“Corrosion resistance of a superhydrophobicsurface on micro-arc oxidation coated Mg-Li-Ca alloy”发表在《Journal of Alloys and Compounds》(C.L Zhang et al. 2017, 728:815-826 )

Highlights:

1 A superhydrophobic surface was fabricated on Mg-1Li-1Ca alloy with SA.

2 SA can infiltrate into the micropores of the MAO and react with substrate.

3 The MAO is sealed with SA and MgSt to block the penetration of aggressive ions.

4 SA coating peels off due to its dissolution, and the stress caused by corrosion.

Fig. 1 SEM morpholgoy and CA (inset) of the MAO coating (a, b) and the MAO/SA 0.5 h, MAO/SA 1 h, MAO/SA 3 h, MAO/SA 7 h coatings (c-f).

Fig. 2 Cross-sectional SEM image of (a) the MAO/SA 7h coating and its corresponding (b-d)EDS mapping of Mg, C and O(e)

Fig. 3  Hydrogen evolution rate of the Mg-1Li-1Ca alloy and its coatings

Fig. 4 Schematic representation of the coating formation mechanisms of the MAO/SA composite coatings

Fig. 5 Schematic representation of the corrosion mechanisms of the MAO/SA composite coatings

相关文献

[1] Purity ofthe sacred lotus, or escape from contamination in biological surfaces. W. Barthlott, C. Neinhuis. Planta,1997, 202(1): 1-8.

[2] Characterization and Distribution of Water-repellent, Self-cleaning Plant Surfaces. C. Neinhuis, W. Barthlott. Annals of Botany, 1997, 79(6): 667-677.

[3] Corrosion-resistant superhydrophobic coatings on Mg alloy surfaces inspired by lotus seedpod. Dongmian Zhang, et al. Advanced Functional Materials, 2017, 27, 1605446.

[4] Fabrication of the superhydrophobic surface on magnesium alloy and its corrosion resistance. Fen Zhang, Changlei Zhang, Liang Song, Rongchang Zeng, Shuoqi Li, HongzhiCui. Journal of Materials Science & Technology, 2015, 31(11): 1139-1143.

[5] Corrosion Resistance of Superhydrophobic Mg-Al Layered Double Hydroxide Coatings on Aluminum Alloys. Fen Zhang, Chang-Lei Zhang, Liang Song, Rong-Chang Zeng, Lan-Yue Cui, Hong-Zhi Cui. Acta Metallurgica Sinica (English Letters), 2015, 28(11): 1373-1381.

[6]Corrosion Resistance of the Superhydrophobic Mg(OH)₂/Mg-Al Layered Double Hydroxide Coatings on Magnesium Alloys. Fen Zhang, Changlei Zhang, Rongchang Zeng, Liang Song, Lian Guo, Xiaowen Huang. Metals, 2016, 85 (6): 1-14.

[7] Corrosion resistance of a superhydrophobic micro-arc oxidation coating on Mg-4Li-1Ca alloy. Lan-Yue Cui, Han-Peng Liu, Wen-Le Zhang, Zhuang-Zhuang Han, Mei-Xu Deng,Rong-Chang Zeng, Shuo-Qi Li, Zhen-Lin Wang. Journal of Materials Science & Technology, 2017, 33: 1263-1271.

链接：曾荣昌发表论文目录（Rong-Chang Zeng's Publications）(2000-)