Study On The Corrosion Resistance Of Non-chromate Organic-inorganic Hybrid Conversion Coating On Aluminium Alloy

Aluminum alloy is known for plenty of favourable properties such as electrical and thermal conductivity, mechanical workability, making them suitable for a wide range of applications in manufacturing industry or marine engineering, which is specifically used in a great variety of shipbuilding, aviation, and pipelines system. In spite of the fact that aluminium alloy could form a self passive film at lower concentration of corrosive medium, which can suppress the dissolution of substrate and the diffusion of oxygen, however, the passivity and stability of this layer are greatly affected by the aggressive ions, in seawater for instance, which could easily cause a serious corrosion subsequently the deterioration of mechanical performance. Therefore, the protection of aluminium alloy is a fundamental academic and industrial concern that received a considerable amount of attention. Employment of chromate passivity technique is the most widespread strategy. Nevertheless, this traditional method has been gradually replaced by occasion of its toxicity. The research in fields of eco-friendly corrosion passivant has been addressed toward the cheap, effective at low or zero environment impact.The aim of this paper is to present the remarkable corrosion inhibiting performance of two novel chrome-free passivity technologies, involving the application of silane-fluorozirconate and thiadiazole-fluorozirconate system, respectively. Through utilizing the orthogonal optimization experiment and the single factor detection, the optimum technological parameters of silane-fluorozirconate chrome-free passivation system have been determined. Meanwhile, the corrosion resistance of passivation film has also been measured by the test of copper sulfate intravenous drip, electrochemical impedance spectrum, polarization curves and neutral salt spray testing, of which the results reveal that the corrosion resistance of chrome-free passivation coating has impressively improved in contrast to the blank samples, and noticeable to be comparable with the chromate passivation film. With the help of surface analysis measurement, the film morphology in high magnification and passivity composition in specific composition have been clarified into a deep in situ insight. For further discussion, this paper studies the effect of three chrome-free passivation coatings which involve the preparation of thiadiazole and fluoroziconate complex on the corrosion resistance of2024aluminum alloy. Results of electrochemical experiments indicate that the corrosion resistance of three kinds of chrome-free passivation film are significantly higher than that of blank sample, compared with the samples obtained from silane-fluorozirconate system, the order of corrosion resistance from large to small as follow:TTTi> TTT2> chrome sample> non-chrome sample> DMTY. The morphology and the component of passivation film are analyzed by SEM, EDS as well as XRD experiments. Directed by the Quantitative Structure Activity Relationship (QSAR), quantum chemical parameters of three compounds are calculated, while the chemical reaction mechanism of three corrosion inhibitors in passivation system has been theoretically elucidated to explain why the protection efficiencies of three kinds of system are distinctive.