Electrochemical study of inhibitor-containing organic-inorganic hybrid coatings on AA2024

Use of organic-inorganic hybrid sol-gel thin films is recently reported among the most promising approaches for the replacement of chromate based pre-treatment methods for high strength structural aluminium parts. To be applied in the aerospace industry, pre-treatments have to meet the demanding requirements and must be compatible to state of the art paint systems. The addition of inhibitive species is desirable for the active corrosion protection and the prevention of sub-surface migration at defect sites of the coating. In the present work hybrid films were produced by the controllable sol-gel route. Corrosion inhibitors were incorporated to the coatings in order to provide active protective effect. The barrier properties and the active corrosion protection on AA2024-T3 have been studied by Electrochemical Impedance Spectroscopy and Scanning Vibrating Electrode Technique. The obtained results were proven by conventional accelerated tests such as neutral salt spray test confirming validity of the mentioned electrochemical techniques for the evaluation of protection efficiency of hybrid sol-gel films. The addition of inhibitors to sol-gel coatings in most cases leads to an improvement of the active corrosion protection but on the other hand it may negatively influences the barrier properties of the films. Therefore, encapsulation of the inhibiting compounds is beneficial in order to combine the good barrier function of the coating with the corrosion mitigating effect of the inhibitors. (C) 2009 Elsevier Ltd. All rights reserved.