Anticorrosion behavior of conversion coatings obtained from unbuffered cerium salts solutions on AA6061-T6

The anticorrosive properties of cerium based conversion coatings deposited on AA6061-T6 alloy by immersion in unbuffered cerium chloride and cerium nitrate solutions in the presence of hydrogen peroxide were investigated and characterized by potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) in 0.5 mol/L NaCl aqueous solution. The microstructure and chemical composition of the protective films were examined by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). It was found that the best corrosion protection was afforded by the samples treated during 600 s in cerium chloride solution at pH values ∼5.5-4, showing higher amounts of cerium and polarization resistance values greater than 10 Ω m2. Moreover, an ennoblement of the corrosion potential and decreasing of the cathodic and anodic currents were obtained compared with the cerium nitrate solutions application. This behavior was attributed to the influence of the deposition parameters such as type of the salt anion, i.e., chelating effect and chaotropic characteristics, pH fluctuations in the conversion solution and deposition time.