Investigate On In Situ Phosphatizing Coatings Of6061Aluminum Alloy

Traditional metal painting technology is a multi-step process, which involves alkaline cleaning, rustremoving, spray or immersion phosphating conversion, sealing, drying and then painting. Phosphating filmand the formation of organic coatings are separated, technological process complex, process parametersmore and operation control hard. In addition, after phosphating treatment, there are still a porosity of about1%-5%in the total metal surface area, the corrosion resistance of organic coatings is not satisfactory. It iseasily to produce toxic solution, heavy metals and other toxic substances in the painting process, which is agreat deal of pollution for environment. Now, an increasing demand for global environmental protectionand energy saving, therefore in situ phosphatizing coatings (ISPC) come into being. This technology is thephosphating reagent added directly to the organic coatings, the process of phosphate conversion andorganic coating film curing take place at the same time in one-step. It effectively reduce the economic costsand operational complexity in the multi-step painting process.On the basis of analyzing the concerned in situ phosphatizing technology in the word, this paperinvestigated in situ phosphatizing organic coatings, which were prepared by incorporating in situphosphatizing reagent (ISPR), an phenylphosphonic acid and organic paint, white alkyd paint, apploied on6061aluminum alloy. It was proved that in situ phosphatizing organic coatings can significantly improvethe corrosion resistance of aluminum alloy and the bonding force with the metal through a series ofelectrochemical experiments. The main work and conclusions of the article were as follows:1. According to the single factor test, to optimize and analyze the different content ofphenylphosphonic acid, organic coating thermal curing temperature and time, the optimum technology of insitu phosphatizing coatings was developed, namely, content of phenylphosphonic acid is2%(mass fraction), the temperature of thermal curing is50℃and the time of thermal curing is8h.2. Compared in situ phosphatizing organic coatings with organic coatings after phosphated andchromated, it was proved that the corrosion resistance of in situ phosphatizing organic coatings is betterthan the organic coatings after phosphated and chromated through polarization curves and electrochemicalimpedance spectrum (EIS) technique. In situ phosphatizing organic coatings can effectively block thepenetration of corrosion particles and inhibit the corrosion reaction of aluminum alloy, moreover, thebonding strength between the coating film and metal is also improved.3. On the basis of in situ phosphatizing technology, the rare-earth-type in situ phosphatizing organiccoatings was prepared by adding different amounts of rare earth chloride (ReCl3) in situ phosphatizingsolution. Different rare earth chlorides had an influence on the corrosion resistance of in situ phosphatizingorganic coatings, and at the same time were compared with each other. The experiment results showed that:①The amount (0.2%, mass fraction) of rare earth chloride can enhance the corrosion resistance of organiccoatings, the optimal effect was LaCl3.②When the amount (0.5%~1.5%, mass fraction) of rare earthchloride is excessive, the corrosion resistance of organic coatings will lower.4. In situ phosphatizing organic coatings was prepared as steel for the metal substrate under the sameconditions, compared with in situ phosphatizing organic coatings prepared as aluminum alloy for the metalsubstrate through the corrosion resistance experiments. The results showed that: the corrosion resistance ofin situ phosphatizing organic coatings prepared as aluminum alloy for the metal substrate is better than insitu phosphatizing organic coatings prepared as steel for the metal substrate, which may be due to the largerionicity of the Al-O bond in the aluminum phosphate film compared to the Fe-O bonds in the ironphosphate film.