Galvanic compatibility of corrosion protective coatings with AA7075 aluminum alloy |
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| Authors: | Z F Lodhi W J Hamer J M C Mol H Terryn J H W de Wit |
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| Affiliation: | 1. Netherlands Institute for Metals Research (NIMR), Mekelweg 2, 2628 CD Delft (The Netherlands);2. Delft University of Technology, Department of Materials Science and Engineering, Mekelweg 2, 2628 CD Delft (The Netherlands);3. Department of Metallurgy, Electrochemistry and Materials Science, Vrije Universiteit Brussel, Pleinlaan 2, B‐1050 Brussels (Belgium) |
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| Abstract: | The galvanic compatibility of aerospace aluminum alloy AA7075 with cadmium (Cd), zinc (Zn), and zinc–cobalt–iron (Zn–Co–Fe, 32–37%Co and 1%Fe) alloys was investigated. A comparison of open circuit potential OCP vs. saturated calomel electrode (SCE)] measurements in 0.6 mM NaCl showed that all coatings would act anodically to AA7075 with an exception of Zn–Co–Fe (37%Co + 1%Fe) alloy which was electropositive to AA7075. During the zero resistance ammetry (ZRA) measurement in 0.6 M NaCl electrolyte the coupled OCP and current density were measured during 7 days of immersion and both Zn and Cd acted anodic and thus sacrificial to AA7075. Galvanic coupling of AA7075 with (37%Co + 1%Fe) Zn–Co–Fe alloy resulted in the consequent dissolution of the AA7075 aluminum alloy. In contrast, Zn–Co–Fe (32%Co + 1%Fe) alloy was found to be anodic to AA7075 during the first 26 h of immersion but after dezincification and cobalt enrichment at the surface became cathodic to the AA7075 aluminum alloy. During coupling with Zn, some pitting was also observed on AA7075. |
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| Keywords: | AA7075 corrosion resistance galvanic coupling zinc alloys Zn– Co– Fe alloys ZRA |
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