| Aluminum and aluminum alloy are widely applied on every field of modern economy; its usage quantity is the second only next to steel material. As it well known, the chromate passivation technique is proverbially used for the corrosion resistance of aluminum and aluminum alloy. However, the chromate passivation films contains hexavalent chrome which is a kind of extremely poisonous to environment and carcinogenic to the body, many countries in the world have released some policies or laws to restrict or forbid the usage of chromate passivation technique and appealed to use chrome-free passivation technique. In the practice choice of chrome-free passivation technique, the titanate and/or zirconate passivation system showed gradually nicer foreground of industrial application, but its corrosion resistance and adhesion to paint are so far from chromate passivation films that it can not meet needs of preparation technique and performance in many usage condition. For the sake of researching and developing environmental-friendly and high-performance and low-cost chrome-free passivation technique, the titanate-zirconate and organophosphonate composite treatment technique was put forward on the base of optimizing and improving the titanate-zirconate passivation technique in this paper. A hydrophobic layers hybridized with the titanate-zirconate films was obtained using chemistry characteristic of an organophosphonic acid to intensify the adhesion to paint and improve the corrosion resistance of the whole coatings system.AA6061 aluminum alloy in this paper was mainly investigated by one-step method, namely, an organophosphonic acid was added to the titanate-zirconate treatment solution as addition reagent and the titanate-zirconate organophosphonate hybrid films was obtained on AA6061 aluminum alloy. The two-step method was studied to contrast the performance and structure of the titanate-zirconate organophosphonate hybrid films obtained by one-step method, namely, the organophosphonic acid as post-treatment reagent was used to block off the titanate-zirconate films on AA6061 aluminum alloy. The paint performance of the titanate-zirconate organophosphonate hybrid films with paint on A356 aluminum alloy and a self-assemble organophosphonate layers with paint on AA6061 aluminum alloy was investigated, too.The morphology, element composition, chemistry state and corresponding mechanism were systematically investigated by scanning electron microscopy with energy dispersive spectroscopy (SEM/EDAX), atomic force microscopy (AFM), laser scanning confocal microscope (LSCM), fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The corrosion resistance and paint performance were explored by the methods of dropping test, neutral salt spray test and electrochemical test.The composition of the treatment solution was designed and optimized by single factor test and orthogonal test; The basic composition and concentration of the treatment solution were confirmed; The kind and concentration of organophosphonic acid were determined; The preparation technique parameters of the hybrid films obtained by one-step method was researched. The corrosion resistance performance of the hybrid films was evaluated by electrochemical test and salt spray test. The electrochemical results show that one-step method is better than two-step method, the hybrid films obtained by one-step method is good as the chromate passivation films. The salt spray test results show that the hybrid films by one-step method without paint is similar to the hybrid films by two-step method without paint. The morphology of the hybrid films was observed by SEM and AFM, the test results show that the hybrid films by one-step method and two-step method are both continuous films. The characterization and structure of the hybrid films were analyzed by FTIR and XPS, the test results show that the structure of the hybrid films by one-step method and two-step method are both hybrid composite structure of the titanate-zirconate films and organophosphonate films. The paint performance of the hybrid films was evaluated by adhesion test, dipping test and neutral salt spray test, the results show the adhesion of the hybrid films to paint is obviously increased compared with the titanate-zirconate films, the blistering and de-painting are effectively restrained, the corrosion performance of the hybrid films is advanced and similar to the chromate passivation films with paint.The performance of the titanate-zirconate organophosphonate hybrid films/paint system on A356 alloy was investigated by dipping test and neutral salt spray test. The results show that the titanate-zirconate organophosphonate hybrid films can improve the adhesion and the corrosion resistance on A356 aluminum alloy.The application of the organophosphonic acid as a self-assemble molecular technique (SAM) on AA6061 aluminum alloy was explored. The aminotrimethylene phosphonate films were formed by aminotrimethylene phosphonic acid adsorption on the surface of AA6061 aluminum alloy. The results show that the corrosion resistance and the adhesion of the aminotrimethylene phosphonate films with paint have a similar performance comparing with the chromate passivation films with paint.To sum up, the structure of the titanate-zirconate organophosphonate hybrid films obtained by one-step method is similar to two-step method, which have particular structure and superior performance. The structure is hybrid composite structure of the titanate-zirconate films and the organophosphonate films. The adhesion to paint of the titanate-zirconate organophosphonate hybrid films is obviously advanced, the blistering and de-painting are effectively restrained, and the corrosion resistance performance is similar to the chromate passivation films with paint. The mechanism of the the hybrid films having superior performance rests with synergy effects between different structure films. This structure make the hybrid films have more superior barrier and insulation, block off infiltration of Cl- ion and improve the corrosion resistance. After coated paint, the organophosphonate films in the structure of the hybrid films can link with the resin in the paint by covalence bond, improve the corrosion resistance of the whole coatings system, block off infiltration of H2O, O2 and Cl" ion, restrain electroosmosis and avoid blistering and de-painting. |
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