Abstract
A chemical conversion coating on 5052 aluminum alloy was prepared by using K2ZrF6 and K2TiF6 as the main salts, KMnO4 as the oxidant and NaF as the accelerant. The surface morphology, structure and composition were analyzed by SEM, EDS, FT–IR and XPS. The corrosion resistance of the conversion coating was studied by salt water immersion and polarization curve analysis. The influence of fluorosilane (FAS-17) surface modification on its antifouling property was also discussed. The results showed that the prepared conversion coating mainly consisted of AlF3·3H2O, Al2O3, MnO2 and TiO2, and exhibited good corrosion resistance. Its corrosion potential in 3.5 wt % NaCl solution was positively shifted about 590 mV and the corrosion current density was dropped from 1.10 to 0.48 μA cm−2. By sealing treatment in NiF2 solution, its corrosion resistance was further improved yielding a corrosion current density drop of 0.04 μA cm−2. By fluorosilane (FAS-17) surface modification, the conversion coating became hydrophobic due to low-surface-energy groups such as CF2 and CF3, and the contact angle reached 136.8°. Moreover, by FAS-17 modification, the corrosion resistance was enhanced significantly and its corrosion rate decreased by about 25 times.
Highlights
Aluminum alloys are widely used in various fields such as aerospace, automotive, transportation, petrochemical, construction and electronics industries due to their high strength, good thermal and electrical conductivity, good plasticity and lack of magnetism [1,2]
Aluminum alloys are vulnerable to pollution by organics, so it is necessary to treat the surface of aluminum alloys before application
The research for chromate conversion coating substitutes has more than 20 years of history, but in the last few years it has become more intense, due to the fact that in 2007 the chromate coatings were banned from European industry except from aeronautics applications that still have a permission to use these treatments
Summary
Aluminum alloys are widely used in various fields such as aerospace, automotive, transportation, petrochemical, construction and electronics industries due to their high strength, good thermal and electrical conductivity, good plasticity and lack of magnetism [1,2]. Lunder et al fabricated a Ti/Zr-based conversion coating on AA6060 aluminum alloys—the results showed that the conversion coating slightly restrained the cathodic activity, but was expected to improve the corrosion resistance of aluminum significantly [14]. Yi et al fabricated a golden Ti–Zr-based conversion coating on AA6063 aluminum alloys; the mechanism of film formation was discussed. Their results found a reduced corrosion current density and a significantly improved corrosion resistance [16]. Zhu et al developed a Ti/Zr/V conversion coating on the surface of aluminum alloy 6063 (AA6063), and reported that its anticorrosion performance and adhesion properties were superior to that of chromate conversion coating [18]. The results indicate that both the anticorrosion performance and the antifouling performance of aluminum alloys are improved
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