The effect of inhibiting molybdate used in anodizing-conversion treatment to improve corrosion protection of AA2030 aluminum alloy in different steps

Abstract

Abstract In this article, different treatment baths for corrosion protection of 2030 aluminum alloy in addition to replacing the hexavalent chromium due to the European recommendation were employed. This work is divided into three steps of treatment: first, anodization using molybdate inhibitor without and with phosphoric acid and, then, pre-oxidation with sodium hydroxide. In the last step, we studied the influence of conversion coating with the combination of sodium molybdate and fluoride on the anodic layer formed on aluminum alloy 2030. In order to characterize the formed layers, we use microstructural characterization (SEM, AFM, and nano-indentation), which allows highlighting the surface condition as well as the morphological distribution, and electrochemical techniques such as potentiodynamic polarization and electrochemical impedance spectroscopy which shows that the anodization treatment of the aluminum alloy with phosphoric acid and sodium molybdate offered better corrosion resistance. This resistance increased with the use of pre-oxidation and then reached a maximum value of 99.8% efficiency with the addition of the molybdate conversion coating which causes an increase in the double layer and gave an alternative possibility of chromium VI.

Keywords

• Corrosion
• Anodization
• Sodium molybdate
• Electrochemical impedance spectroscopy
• Potentiodynamic polarization