A room temperature cured sol-gel anticorrosion pre-treatment for Al 2024-T3 alloys

The inherent reactivity of the Al-Cu alloys is such that their use for structural, marine, and aerospace components and structures would not be possible without prior application of a corrosion protection system. Historically these corrosion protection systems have been based upon the use of chemicals containing Cr(VI) compounds. Organic-inorganic hybrid silane coatings are of increasing interest in industry due to their potential application for the replacement of current toxic hexavalent chromate based treatments. In the present study, a hybrid epoxy-silica-alumina coating with or without doped cerium nitrate has been prepared using a sol-gel method. The hybrid coatings were applied by a dip-technique to an Al-Cu alloy, Al 2024-T3, and subsequently cured at room temperature. The anticorrosion properties of the coatings within 3.5% NaCl were studied using electrochemical impedance spectroscopy (EIS), and conventional DC polarisation. An exfoliation test method involving immersion in a solution of 4 M NaCl, 0.5 M KNO3 and 0.1 M HNO3 was also used. The cerium nitrate doped sol-gel coating exhibited excellent anticorrosion properties providing an adherent protection film on the Al 2024-T3 substrate. The resistance to corrosion of the sol-gel coating was also evaluated by analysing the morphology of the coating before and after corrosion testing using scanning electron microscopy. (c) 2007 Elsevier Ltd. All rights reserved.