Assessment of corrosion inhibition performance of quaternary ammonium based dicationic ionic liquids for AZ91D magnesium alloy in NaCl solution

Quaternary ammonium based ionic liquids (ILs) are considered as good corrosion inhibitors to protect substrates of metals such as carbon steel, copper and aluminum alloys against corrosion. However, studies applying them to the corrosion protection of magnesium (Mg) alloys still remain scarce. Herein, in this work, three quaternary ammonium based dicationic ILs, namely [DMBAB][MOPS] 2 , [DMBAB][Phe] 2 and [DMBAB][Trp] 2 were synthesized and applied as corrosion inhibitors to improve the corrosion protection ability on AZ91D Mg alloy in 0.5 wt% NaCl solution. Their corrosion inhibition performances were evaluated by electrochemical measurements, and the relevant corrosion results were investigated by extensive characterizations including scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Results show that the [DMBAB][Trp] 2 obtains an 88.8  % inhibition efficiency for AZ91D Mg alloy in 0.5 wt% NaCl solution, clearly higher than those of [DMBAB][Phe] 2 (80.4 %) and [DMBAB][MOPS] 2 (81.7 %). This suggests that [DMBAB][Trp] 2 presents the best corrosion protection ability on AZ91D Mg alloy among these ILs considered here, which is associated with the largest steric body and the most active adsorption sites of [DMBAB][Trp] 2 in comparison with other two compounds, hence resulting in a highest surface coverage. The present work offers a guidance for understanding the structure–property relationship of quaternary ammonium based dicationic ILs through a convenient, economical and effective way with a promising application in the field of material protection.