Corrosion resistance of Al and Al–Mn thin films

• Corrosion resistance of Al was improved by alloying with Mn in NaCl aqueous solution.
• The pitting potential increased with Mn concentration.
• Amorphous Al-Mn exhibited the best pitting resistance during short term tests.
• Nanocrystalline Al-Mn showed the highest corrosion resistance over long term test.

Magnetron-sputtered aluminum (Al) and aluminum–manganese (Al-Mn) films with structures ranging from nanocrystalline to amorphous were obtained by tuning the Mn% up to 20.5 at.%. Corrosion behavior of the films was investigated in 0.6 M and 0.01 M NaCl aqueous solutions by potentiodynamic polarization and electrochemical impedance spectroscopy. Pitting corrosion was found to be strongly affected by alloy composition. The amorphous Al–20.5 at.% Mn exhibited the best pitting resistance during short term exposure. However, over longer immersion in 0.01 M NaCl up to 108 h, nanocrystalline Al–5.2 at.% Mn showed the highest corrosion resistance. The dual-phase Al-11.5 at.% Mn alloy was found to have higher nominal corrosion rate compared to its nanocrystalline or amorphous counterparts.