Alkaline activation of Al 7075-T6 for deposition of cerium-based conversion coatings

作者：Joshi Simon^*; Fahrenholtz William G; O'Keefe Matthew J

来源：Surface and Coatings Technology, 2011, 205(17-18): 4312-4319.

DOI：10.1016/j.surfcoat.2011.03.073

• Cerium-based coatings
• Alkaline activation
• Aluminum alloys
• Electrochemical analysis
• Corrosion

The effect of alkaline activation on the morphology and corrosion performance of cerium-based conversion coatings deposited on Al7075-T6 was studied. Prior to coating deposition, alloy panels were activated in aqueous solutions containing Na(2)CO(3) or NaOH. Scanning electron microscopy indicated that as-deposited coatings on Na2CO3 activated substrates had fewer surface cracks, fewer craters, and were more uniform than those activated with NaOH. Post-treatment of coatings in a NaH(2)PO(4) solution improved the corrosion resistance and reduced the number of visible cracks; however, some regions still exhibited large cracks (>0.5 mu m wide). Subsurface crevices were found under craters and regions with large cracks, which were fewer for coatings on Na(2)CO(3) activated substrates compared to coatings on NaOH activated substrates. Electrochemical impedance spectroscopy testing showed that post-treated coatings on Na(2)CO(3) activated panels had total impedance of similar to 200 k Omega cm(2) compared to similar to 50-100 k Omega cm(2) for coatings on NaOH activated panels. Alkaline activation promoted deposition of corrosion resistant coatings with Na(2)CO(3) activation exhibiting the best corrosion resistance and the least amount of subsurface damage.

• 出版日期2011-5-25