Aluminum Electroplated from Ionic Liquids as Protective Coating against Steel Corrosion

An ionic liquid electrolyte was prepared by mixing 66.7 mol% anhydrous AlCl3 and 33.3 mol% 1-Butyl-3-methylimidazolium chloride (BMIC) in AlCl3 BMIC melt. The effect of temperature, current density, and amount of toluene additive on the electroplating process was studied. The characterization of the deposited aluminum was performed using scanning electron microscopy (SEM/EXD) and X-ray diffraction (XRD) techniques. The corrosion resistance of the deposited Al coatings was studied by electrochemical testing. The results showed that a dense and well adherent aluminum coating was obtained under the conditions of 45±2 ℃, current density of 20～25 mA/cm2, and content of toluene 5～12 ml/L. All of the electrodeposits exhibited a strong preferred (200) crystallographic orientation, and the preferred (200) orientation was enhanced with the increase of current density. By depositing Al coating at 25 mA/cm2, the corrosion potential Ecorr and the corrosion current density Icorr of Fe substrate moved to negative direction from -669 mV (SCE) to -1019 mV (SCE), from 65.7 μA/cm2 to 6.07 μA/cm2 separately, comparable to those of pure Al (Ecorr=-1031 mV (SCE), Icorr=1.24 μA/cm2).