Electrochemical noises of LC4, LY12 and pure Al in NaCl solution

Electrochemical noise (EN) test of aluminum alloys LC4, LY12 and pure aluminum in 2.0% (mass fraction) NaCl solution (pH=7.01) was reported. The potential fluctuation of the electrodes was recorded in time domain and simultaneously processed by fast Fourier transform method to gain spectra power dendsity (SPD) curves in frequency domain. It is found that EN characteristic varies with materials, that is, in time domain, pure aluminum and LC4 can stochastically exhibit sudden potential drop, which results in a sharp peak in potential-time curves, but LY12 does not. And the three features in SPD curve: W (white noise level), f(c) (cutoff frequency), and K (the slope of the high frequency domain), all change with the corrosion process and reach their extremum when pitting occurs. Any single parameter cannot correctly predict the strength and trend of pitting. However, two parameters S-E and S-G derived from the SPD curves can correctly predict whether pitting has occurred or not. That is, for different materials, pitting corrosion usually occurs when S-E >5 and S-G <1,