Electroplating of mild steel by aluminium in a first generation ionic liquid: A green alternative to commercial Al-plating in organic solvents

In this paper we report on the electroplating of mild steel by aluminium in a first generation ionic liquid [EMIm]Cl/AlCl3 (40/60 mol.-%). The study was performed by means of cyclic voltammetry and galvanostatic polarization complemented by SEM/EDAX and optical microscopy. The results show that the pretreatment of the substrates plays a key role in the coating adhesion. The aluminium coating made on a conventionally pretreated mild steel substrate is of high quality but it does not exhibit good adherence to the substrate. However, we have found that an in situ electrochemical etching of the substrate by anodic polarization prior to electrodeposition leads to well adherent Al coatings of mild steel which resist even mechanical scratching. This is due to dissolution of the pre-formed iron oxide layer and the subsequent re-deposition of iron or Fe–Al alloy formation prior to Al bulk deposition resulting in excellent adhesion. It is also shown that with the electrochemical pretreatment in the ionic liquid not only steel sheets but also complex shapes like e.g. screws can be coated with well adherent aluminium.