Abstract
In this study, a vanadium (V) and tannic acid-based composite conversion coating (VTACC) was prepared on 6063 aluminum alloy (AA6063) to increase its corrosion resistance. The surface morphology and compositions of the VTACCs were characterized using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS). The corrosion resistance of the coatings was investigated by linear polarization and electrochemical impedance spectra (EIS). The self-healing ability of the coating was detected by SEM, EDS, and scanning vibrating electrode technique (SVET) measurements. The coating mainly consisted of metal oxides, including Al2O3, VO2, V2O3, and V2O5, and metal organic complexes (Al and V-complexes). The electrochemical measurement results indicated that the best corrosion resistance of VTACC was acquired when the treatment time was 12 min. Furthermore, because a new coating with vanadium rich oxide was developed on the scratch area, artificial scratch VTACC surfaces were repaired after several days of immersion in 3.5-wt% NaCl solution.
Highlights
Aluminum (Al) alloys have numerous industrial applications because of their high mechanical performance and low density (Dursun and Soutis, 2014)
scanning electron microscopy (SEM) images and energy dispersive spectrometry (EDS) results of AA6063 samples after immersion in VTA-based solution for 5, 10, 15, and 20 min exhibited that mechanical scratches, granules, and long grooves were observed on samples surfaces, which was mainly produced by brittle particles fracturing and/or debris embedded in the substrate as it was processed (Figure 1A) (Koroleva et al, 1999)
When the treatment time increased to 10 min, scallops on the sample’s surface became shallow due to the formation of a thicker vanadate and tannic acid composite conversion coating (VTACC) coating on the alloy (Figures 2C,D)
Summary
Aluminum (Al) alloys have numerous industrial applications because of their high mechanical performance and low density (Dursun and Soutis, 2014). Surface modification treatments, for example, electroplating (Chen et al, 2011), anodization (Bertram et al, 2014), micro-arc oxidation (Li et al, 2020), and chemical conversion (Twite and Bierwagen, 1998), have been developed to improve the corrosion resistance of Al alloys. Among these methods, the conversion treatment technique is known for its low-cost and operation simplicity. Various non-chromate conversion coatings have been exploited in the last few decades, including phosphate (Shida et al, 2003; Sheng et al, 2010), molybdate (Huang et al, 2019; Chen and Xu, 2021), rare-earth metal salts (Aziz et al, 2011; Zuo et al, 2014), vanadate (Vega et al, 2011; Niu et al, 2014), and zirconate and/or titanate (Lunder et al, 2004; Guan et al, 2011; Yi et al, 2012; Zuo et al, 2015)
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