Effect of Inhibitors on Pitting Corrosion of AA6063 Aluminium Alloy Based on Electrochemical Noise

The pitting corrosion of AA6063 aluminum alloy in 3%(w) NaCl solution was investigated by electrochemical noise(ECN),electrochemical impedance spectroscopy(EIS),and polarization curves.Inhibition of nucleation and propagation of metastable pits by inhibitors,such as CeCl3,Na2CrO4,and 8-hydroxyquinoline(8-HQ),was evaluated based on ECN data statistics.It was found that the local pH could be over 8.4 near the cathode phase(Al-Si-Fe) due to dissolution of Al matrix,leading to preferential deposition of Ce(OH)3 on the surface of the cathode phase,thereby inhibiting the cathodic process of pitting corrosion.The average electric charge(q) of metastable pits decreased with increasing the corrosion inhibitor concentration,but the average lifespan of noise transients remained almost constant,indicating that Ce 3+ ions did not accelerate the rehabilitation of metastable pits directly,but reduced the dissolution rate of Al inside active pits.However,CrO4 2ions not only accelerated the rehabilitation of metastable pits,but also reduced the nucleation rate of the AA6063 aluminum alloy.In contrast,8-HQ acted as an effective corrosion inhibitor for AA6063 aluminum alloy through formation of insoluble chelate films with Al3+ ions and Mg2+ ions,but failed to enhance the pitting corrosion resistance of the aluminum alloy.