A Combined Experiment and Modeling Analysis of ASTM G85 WB Accelerated Corrosion Testing of Galvanically Coupled Sensitized AA5456-H116 and CDA 706 Cupronickel

Abstract

AA5456-H116 undergoes accelerated localized corrosion when in a galvanic couple with cupronickel alloy C70600 (CDA 706) during ASTM G85 Appendix 2 Wet Bottom (G85 WB) testing. Surface and subsurface damage of AA5456-H116 and the region of protection of the C70600 were investigated and quantified after 31 d (124 cycles). These results were compared to finite element modeling results investigating relative humidity (RH) and water layer (WL) thickness. The best fit between experimental results and the modeling results was found when modeling assumed that a 3,000 μm water layer was formed during the spray portion at the start of each G85 cycle, with thinner water layers present during the decreasing RH portion of the cycle, which led to intergranular corrosion attack that was primarily focused in the proximity of the C70600/AA5456-H116 interface, but extending along the AA5456-H116 surface for some distance. The high-water layer thickness is likely the result of the corrosion product formation that traps additional electrolyte than would be present on a clean surface.