Eco-Friendly Electrodeposition of Al-Zn Alloy from AlCl₃-Urea Deep Eutectic Solvent

Abstract

The electrodeposition of Al-Zn alloy from an aluminium chloride-urea (AlCl3-urea) deep eutectic solvent (DES) containing 0.1 M ZnCl2 near room temperature was investigated. Cyclic voltammetry demonstrates that Al and Zn can be co-deposited, but the presence of Zn(II) restrains the reduction of Al(III). Linear sweep voltammetry reveals that increasing temperature facilitates the reduction of Zn(II) and Al(III), but the promotion effect on the Zn(II) reduction is greater than that on Al(III) reduction. Chronoamperometry analysis indicates that the electrocrystallization of Al-Zn alloy on a glassy carbon electrode follows instantaneous nucleation, which is similar to that of pure Al. Scanning electron microscopy shows that the obtained alloy coating is smooth but not compact. With the increase of temperature, the content of Zn in deposits increases, the grain grows up and the microstructure transforms from granular to cluster structure. Energy-dispersive spectroscopy and X-ray diffraction analysis prove that the deposits are pure Al-Zn alloy and composed of α phase and η phase. Tafel polarization test confirms the as-prepared alloy coating with higher Zn content (45 wt.%) possesses excellent corrosion resistance. All these findings promise an eco-friendly and simple route to produce the Al-Zn alloy coating with excellent corrosion resistance near room temperature.