Effect of pH on Electrochemical Behavior of 2024-T351 Aluminium Alloy in NaCl Solution

Potentiodynamic polarization test and electrochemical impedance spectroscopy(EIS) were applied to investigate the effect of pH on the electrochemical behavior of 2024-T351 aluminium alloy in 0.6 mol·L-1 NaCl solution. The results showed that the passive film on the surface of aluminium alloy was stable in NaCl solition when pH=5~7 and the Nyquist plots were characterized by two distinct capacitance arcs. With the decrease of pH, the cathodic current density increased, the passive film became thinner, both Rox and Rct decreased. In acid (pH=3) NaCl solution, there was only one capacitance arc in Nyquist plot, indicating that the passive film was not stable with the decrease of pH. As a result, the matrix alloy was exposed to solution directly and subject to corrosion, and the polarization curves showed the electrochemical characteristics of 2024-T351 aluminium alloy.