This paper aims at designing a simple corrosion resistant vanadia based chemical conversion coatings as alternative to the commonly used process involving toxic hexavalent chromate for high strength AA2024 T3 alloy. The proposed coating is environmentally acceptable as a diluted vanadate solution has been used at room temperature for a short treatment time. The effect of vanadia solution pH was investigated in 3.5% NaCl using different electrochemical techniques such as electrochemical impedance spectroscopy (EIS), linear polarization and cyclic voltammetry. Results showed that vanadia coatings prepared by dissolving 10 gram of vanadate salt per liter at the neutral pH (about 7) have proven to offer the best inhibition to localized corrosion after one week of immersion in chloride containing solution. The optimum pH of vanadia treatment was measured as a function of corrosion inhibition characteristic. A vanadia based surface treatment of self-healing characteristics prepared by simple industrially-applicable free immersion technique was proposed. The autonomic healing concept was investigated using scanning electron microscopy (SEM) with energy dispersive using X-ray (EDS) and macroscopic images after immersion in aerated NaCl solution.
Extensive research efforts have been invested during the last decades for improving the localized corrosion resistance of series 2000 aluminum alloys due to the strong impact of such materials in many strategic industries such as aerospace, automobile and marine applications. The presence of some alloying elements such as copper particularly improves the strength of series 2000 aluminum alloys. However, the pitting corrosion attack increases due to the galvanic couples between Al and Cu. Typically, uniformly distributed compact coatings of thickness about 1 to 1.2 micrometers were deposited. Depositions are achieved in 10 minutes and use commercially available chemical, materials and equipment, making the overall process compatible with industrial operations such as those employed by current aircraft manufacturers.