Electrodeposition of Bright Al-Zr Alloy Coatings from Dimethylsulfone-Based Baths

Abstract

Electrodeposition of Al coatings from dimethylsulfone (DMSO₂)-AlCl₃ baths with the addition of ZrCl₄ was studied. Although pure Al coatings electrodeposited from the bath without ZrCl₄ are lusterless, bright and smooth coatings were obtained when the ZrCl₄ content in the baths was 0.005–0.015 mol per 10 mol DMSO₂. The Zr content in the coatings varied up to 3.5 at% in proportion to the ZrCl₄ content in the baths. The bright Al-Zr alloy coating showed high reflectance of 50–80% in the wavelength range of 450–1000 nm, whereas that of the matte pure Al coating was 10–20%. Morphological observations confirmed a reduction in the grain size of Al and surface leveling caused by the addition of ZrCl₄ to the baths. Moreover, a strong 〈100〉 preferential orientation of Al crystals was observed for the bright coatings. The bright coating containing ∼3.5 at% Zr had a higher corrosion potential by 0.1 V than the pure Al coating.