6533b7d9fe1ef96bd126bdf4

RESEARCH PRODUCT

Influence of mass transport on the competition between corrosion of aluminium alloy surface and the release of primer containing inhibitors : validation of a corrosion sensor concept

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The conventional aircraft paint scheme for corrosion protection of aluminum structures is partly based on application of a primer containing inhibitors. In such coatings, release of the inhibiting species enables fast healing of a bare metal surface after a mechanical damage of the protective layers. Nevertheless, considering possible depletion of inhibitors by uncontrolled leaching, it appears important to estimate the corrosion risk integrating “corrosion” sensors in the structure. The objective of this work was to understand the operating mode of a sensor simulating a damaged paint coating whose concept is based on the competition between the triggering of localized corrosion and the passivation of a bare 2024 alloy. The behavior of this massive alloy and Al-Cu solid solutions (the active metallic slots of the sensor) was studied in chloride solution in presence or not of inhibitor ions at different concentrations.Varying the size of a cut-edge electrode coated on both sides, the effectiveness of these inhibitors was demonstrated detecting the microstructural corrosion triggering or its inhibition, by mapping surface pH. Combining these chemical probing with in situ observations it was possible to confirm the nature of the limiting steps controlling the competition between corrosion and passivation. These analyzes highlighted that to quantify this competition, the triggering of the microstructural corrosion represents a key factor which is not possible to mimic by the response of the solid solutions.The existence of a threshold value for the distance between the inhibitor source and the area to be passivated has been confirmed by simulating the mass transport of inhibiting species which appear to be dependent of the release rate of inhibitors.