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 R_ox and R_ct 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.