ABSTRACT

AA2024/Carbon Fiber Reinforced Polymer (CFRP) galvanic couple has been studied under a dynamic electrolyte droplet from both numerical and experimental points of view. A NaCl droplet (3.5 wt.% initial concentration) was used as an electrolyte with controlled temperature (24.5 °C) and relative humidity (83.5%). The evaporation of the electrolyte was monitored by Scanning Kelvin Probe (SKP) for 24h, mimicking atmospheric corrosion phenomena. The electrochemical potential and the high of the droplet were continuously monitored. The finite element analysis included geometry, temperature, potential, aluminum compounds, and pH fields together with both electrochemical and physicochemical boundary condition types. Experimental and numerical findings presented good correlations.

INTRODUCTION

As previously reported,1-6 the gap between electrochemical measurements for systems under bulk conditions and those under thin film layers of electrolyte is still important. Under thin film layers, it is not straightforward to take advantage of the typical three-electrode cell to electrochemically characterize a metallic surface under corrosion. Only a few localized electrochemical techniques are able to achieve measurements under thin films of moisture. It is important to bear in mind that the mechanism for corrosion under thin films is fully different from corrosion on bulk electrolytes and it is not valid to predict the behavior of the former system by extrapolating the latter. Given this situation, mathematical simulation has become a powerful tool to better understand the corrosion behavior of both systems under thin film layers and into bulk electrolytes. 7-8 On the other hand, it is important to point out that although many numerical 7-11 and experimental 12-14 studies have been reported over the last decade (regarding aluminum alloys/CFRP galvanic interactions), the works are significantly reduced 7,8,10 when modeling the AA2024/CFRP galvanic couple in atmospheric conditions.

Under such conditions, the electrolyte thickness varies continuously from a few micrometers up to some millimeters. Faced with this situation, mathematical models are becoming more and more complex and, indeed, just a few examples of them, that include a robust electrochemical model in dynamic electrolytes, are available in the literature.3,4,6,7,8 Our research group has recently published a couple of investigations in this regard, obtaining encouraging results. 7-8

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