Electrochemical evaluation of AA6061 aluminum alloy corrosion in citric acid solution without and with chloride ions

• Corrosion rate of AA6061 in citric acid solution increased with increasing temperature from 10 to 70 °C.
• An increase in corrosion rate in the presence of NaCl compared to its absence was observed.
• The lowest corrosion rate was observed in neutral solutions both in the absence and presence of NaCl.
• In alkaline solutions, addition of NaCl had no significant effect on the corrosion rate.

This paper seeks to study the corrosion behavior of Al alloy AA6061 in solutions containing 0.1 M citric acid as a food additive without and with 0.5% NaCl using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and electrochemical noise (EN) techniques. The results showed that the corrosion rate increased with increasing temperature from 10 to 70 °C both in the absence and presence of NaCl. Meanwhile, an increase in corrosion severity in the presence of NaCl compared to its absence was observed. An increase in pH value from 2 to 7 resulted in a decrease of corrosion rate. At pH 7 the protective oxide film has low solubility and hence the highest corrosion resistance was observed in neutral solutions. In alkaline solutions a general corrosion can occur by hydroxide ions attack. The corrosion behavior of AA6061 was the same in solutions at pH 9, with or without Cl− ions. This is due to the fact that the pH value was equal to the isoelectric point of oxide film. These results which obtained from potentiodynamic polarization and EIS techniques were in accordance with those obtained from EN method. Scanning electron microscope (SEM) images of the samples supported the above conclusions.