The physical, chemical, and electrochemical properties of different variants of a commercial (SurTec 650) trivalent chromium process conversion coating formed on AA7075-T6 are reported on. Comparison of immersion and spray-on application were undertaken. Three different variants of the TCP coating were studied: 650 E, C and V. ICP-OES revealed similar concentrations of Cr for all three coating variants but differences in Zr, Zn, S (likely as sulfate), and Fe among the three. Both application methods produced coatings similar to those seen for other commercial TCP coatings, with a nodular coating morphology. X-ray emission lines indicated that the compositions mainly differed through increased Cr and Ca in V and increased F and Zr in C. Raman spectroscopy indicates a slightly different chromium oxide bond present in the spray coated specimens, which needs to be verified and further examined. The coating roughness and pit depths were determined from profilometry to be statically higher than uncoated specimens for only the 650C composition, due to a less consistent and conformal coating, while 650E and V were equivalent to the uncoated specimens indicating a conformal and continuous film. The film thickness was determined from ellipsometry measurements to be between 40-90 nm for all specimens. Over a seven-day drying period, water contact angles on all films statistically increased from hydrophilic to hydrophobic regions, indicating better primer adhesion and more continuous films on specimens aged for longer time periods. All coating variants produced more active OCPs (< -0.25 V vs Ag/AgCl), indicating cathodic protection, compared to uncoated AA7075 (-0.22 V) in Na2SO4. All coating variants produced more noble OCPs (> -0.67 V), indicating anodic protection, compared to uncoated AA7075 (-0.7 V) in NaCl. In Na2SO4, all coatings provided significantly lower anodic (<1.5 μA/cm2) and cathodic currents (<1.5 μA/cm2) when compared to uncoated AA7075 (2.5 μA/cm2 anodic and 19 μ/cm2 cathodic). 650 E showed the lowest anodic and cathodic currents when applied through both spray and immersion (< 0.5 μA/cm2). In NaCl, all coatings still provided significantly lower anodic (<1.5 μA/cm2) and cathodic currents (<10 μA/cm2) when compared to uncoated AA7075 (6.5 μA/cm2 anodic and 25 μA/cm2 cathodic). 650 E showed the lowest anodic currents when applied through both spray and immersion (< 1 μA/cm2), but cathodic currents were suppressed equally for all coatings. In Na2SO4, all coatings provided significantly higher polarization resistances (>500 kΩ⸱cm2) when compared to uncoated AA7075 (<80 kΩ⸱cm2). 650 E showed the highest polarization resistance when applied through both spray and immersion and modeled with an equivalent circuit (>3,500 kΩ⸱cm2). In NaCl, all coatings again provided significantly higher polarization resistances (>40 kΩ⸱cm2) when compared to uncoated AA7075 (<10 kΩ⸱cm2). Spray 650 E showed the highest polarization resistance when calculated from a short linear sweep around the open circuit (>150 kΩ⸱cm2). Overall, the best corrosion protection was found with both spray coated and immersion coated 650 E, of which the immersion coating provided the most reproducible protection.Accelerated degradation tests on coated samples showed that the immersion and spray coated 650 E protected against the most corrosion when compared to uncoated metals samples.The accelerated degradation tests on a cross comparison of TCP and NCP coatings produced by various manufacturers showed that the 650 E composition performed just as well as the other TCP variants. Luster-On and Chemeon brand TCP coatings performed the best, which correlated with the highest Cr concentrations found in those coating baths.
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