Corrosion and electrochemical evaluation of an Al–Si–Cu aluminum alloy in ethanol solutions

• AC impedance spectroscopy can effectively reveal the corrosion of Al in ethanol.
• The addition of 10 vol.% water or acetic acid increases ethanol corrosivity to Al.
• Al–Si–Cu–Mg precipitates in the Al alloy are susceptible to the corrosion attack.

The corrosion of aluminum alloy AlSi8Cu3Fe(Zn) in ethanol and ethanol solutions containing 10 vol.% water and 10 vol.% acetic acid, respectively, was investigated by means of electrochemical impedance spectroscopy (EIS), polarization curve, immersion, optical microscopy, scanning electron microscopy and element mapping. The Al alloy in the ethanol and its solutions exhibited a capacitive loop in the measured Nyquist EIS spectra at high frequencies, which can be attributed to the ethanol’s dielectric response. Addition of 10 vol.% acetic acid increased the ethanol corrosivity more significantly than the same amount of water addition. The Al–Si–Cu–Mg precipitated zones in the alloy were susceptible to corrosion attack due to the micro-galvanic effect by the Cu-containing precipitates.