镁合金超疏水磷酸盐化学转化涂层的制备与耐蚀性能

Preparation and Corrosion Resistance of Superhydrophobic Phosphate Chemical Conversion Coatings for Magnesium Alloys

目的研究超疏水改性处理对磷酸盐化学转化涂层耐蚀性的影响,利用PA和Ce3+的螯合作用及低表面能物质的修饰提升涂层的防护性能。方法将仿生超疏水技术和化学转化技术相结合,对传统的磷酸盐化学转化膜进行后处理改性,在镁合金基体上制备了具有超疏水效应的磷酸盐化学转化膜。通过扫描电子显微镜、红外光谱、接触角测试、电化学测试等方法研究改性后涂层的微观形貌、润湿性和耐蚀性。结果SEM结果显示,经过后处理改性后,磷酸盐化学转化膜(PCC)表面的缺陷被有效封堵,膜层致密性显著提高。接触角测试结果表明,改性后膜层的静态水接触角高达156.5°,滚动角低至5°,呈现出优异的超疏水性能。电化学测试结果显示,后处理改性后的超疏水膜层的防护性能显著提高;相较于PCC膜层,超疏水膜层的腐蚀电流密度降低了1个数量级,低频阻抗模值则提高了1个数量级,并且经过12 d浸泡后其低频阻抗模值仍然高于104Ω·cm^(2)。中性盐雾测试结果表明,改性后涂层的耐盐雾性能大幅提升,耐盐雾超过100h。结论该涂层展现出了优异的憎水性能和良好的自清洁性能,能够为基体提供高效且持久的腐蚀防护。

Magnesium(Mg)alloys are promising materials for a number of applications in aviation,spaceflight,high-speed rail and automotive industry due to their combination of light weight,excellent shock absorption and recyclability.However,the relatively high corrosion susceptibility of Mg alloys seriously restricts their widespread use.Use of reliable surface protection coatings is an effective method to prolong the service life of Mg alloys and break through the bottleneck of Mg alloy application.Phosphate conversion coatings(PCC)stand out among lots of surface protection technologies for Mg alloys due to its advantages of simplicity,high efficiency and green environmental protection.However,the defects and micro-cracks on the surface of PCC provide a permeable path for water and aggressive ions in a corrosive environment,thus seriously weakening the corrosion protection ability of PCC.Earlier studies have focused on improving the density of PCC by optimizing the process,but in practice the effect on enhancing the durability of PCC is not satisfactory.At present,the construction of high corrosion resistance coatings by integrating PCC with other surface treatment technologies is a research hotspot in the field of Mg alloy corrosion protection.Water is an important factor that causes electrochemical corrosion of magnesium alloys,so hydrophobic treatment is an effective measure to strengthen its corrosion resistance.In recent years,the superhydrophobic surface inspired by lotus leaf has shown great competitiveness and application potential in the field of metal corrosion protection due to its excellent hydrophobic properties.As an environmental-friendly organic phosphonic acid,phytic acid has strong chelating ability with metal ions to generate insoluble chelating precipitate.Based on this characteristic,the work aims to develop a simple,efficient,cheap and eco-friendly cyclic self-assembly process and prepare a superhydrophobic composite coating on Mg alloy matrix by combining PCC.By combining biomimetic superhydrophobic technology and chemical conversion technology,the traditional phosphate chemical conversion film was modified by post-treatment,and the superhydrophobic phosphate chemical conversion film was prepared on Mg alloy matrix.The SEM results showed that the defects of PCC were effectively sealed and film density was significantly improved after the modification.The contact angle test results showed that the modified film presented excellent superhydrophobicity with the static water contact angle as high as 156.5°and the rolling angle as low as 5°.Electrochemical test results showed that the corrosion resistance of modified superhydrophobic film was significantly increased.Its corrosion current density decreased by one order of magnitude and its low-frequency impedance modulus(|Z|0.01 Hz)increased by one order of magnitude,and the|Z|0.01 Hz was still higher than 104Ω·cm^(2) even after 12 d of immersion.The salt spray test indicated that the modified superhydrophobic coating withstood salt spray for more than 100 h.In addition,due to the barrier effect of the"air cushion",the coating exhibited excellent hydrophobic and self-cleaning properties.Therefore,it has potential application value in industrial production due to its simple preparation process and readily available raw materials.