The reliability of electrochemical noise and current transients characterizing metastable pitting of Al–Mg–Si microelectrodes

• Current transients to characterize metastable pitting of an Al alloy are studied.
• The current transient measurement can detect small charge associated with nano-pits.
• The true pit volume is much larger than those determined by current transients.
• Pitting events at Fe-rich cathodic particles are much larger than the spike number.

Current transient measurements and electrochemical noise (EN) method have been used to characterize the metastable pitting events for Al–Mg–Si microelectrodes (diameter 50 μm) in deaerated neutral 0.5 M NaCl solution. The results are compared with those obtained by atom force microscopy and scanning electron microscopy. The pit numbers determined by shot noise analysis at open circuit potential and by current transient analysis at −1.2 V (SCE) are both significantly less than those determined by corrosion morphology image analysis. These results indicate that larger discrepancies can be introduced if the anodic and cathodic reactions localize severely on the same electrode.