Active and passive protection of AA2024-T3 by a hybrid inhibitor doped mesoporous sol–gel and top coating system

• The use of a two-layer coating system is a promising strategy to protect the metal.
• Benzotriazole is released from the mesoporous layer once the coating system is damaged.
• The formation of an inhibitive film within the scratch slows down corrosion processes.
• The electrochemical micro-cell is a useful technique to evaluate the self-healing ability within the defect.

In the present investigation, a two-layer coating system was developed in order to protect 2024 aluminium alloy against corrosion. At the metal interface, a silica mesoporous thin film was used to offer storage and release functionalities for benzotriazole inhibitive molecules (active protection). An acrylic top coat was then applied as a barrier layer against corrosive species (passive protection). Various electrochemical techniques were employed to evaluate the anticorrosion performance of the coating system. Amongst them, the scanning vibrating electrode technique (SVET) and the scanning electrochemical microscopy (SECM) showed a slowdown of corrosion processes occurring within the damaged coating area. The acquisition of anodic polarization curves inside the scratch through the use of an electrochemical micro-cell allowed to correlate this enhancement in the corrosion protection with the formation of an inhibitive film. Upon a through-coating damage, the mesoporous reservoir comes into contact with the aggressive electrolyte and benzotriazole molecules are able to be released and to inhibit corrosion of the bare metal exposed in the scratch. The work demonstrates the potential of mesoporous films as reservoir for inhibitive species and its efficiency for controlled release of the inhibitor. Furthermore, the work demonstrates the added value of electrochemical micro-cell measurements to highlight active corrosion protection in coating defects due to inhibitor doped coating systems.

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