Assessing the corrosion resistance of binary Al–Sc alloys in chloride-containing environment

The corrosion behaviour of binary Al–Sc alloys (Al-0.3Sc and Al-1Sc, wt%) is investigated in de-aerated 0.6 M NaCl solution, performing potentiodynamic polarisation, potentiostatic transients and electrochemical impedance spectroscopy (EIS) measurements complemented with scanning electron microscopy (SEM). In the presence of chloride ions, both Al–Sc alloys experience localised corrosion (pitting). However, increasing Sc alloying addition leads to an increase of the breakdown potential and the extent of passivation domain, indicating improved resistance to initiation of pitting corrosion. Furthermore, EIS measurements performed at the breakdown state evidenced a higher Rct and a lower depression angle value for the Al-1Sc alloy compared to the Al-0.3Sc one, confirming its better localised corrosion behaviour. Spatial distribution and volume fraction of the Al3Sc secondary phase are microstructural features which play a very important role in determining the corrosion resistance of the Al-1Sc alloy.