Stirring effects on aluminium coatings electrodeposited in ionic liquids

Abstract

Aluminium coatings were electrodeposited on Fe9Cr1Mo steel from AlCl₃–1-ethyl-3-methyl imidazolium chloride ionic liquid at room temperature and the effect of solution stirring on deposition rate, preferred crystal orientation, surface morphology and roughness have been investigated. Aluminium coating could not be obtained in the unstirred solution for a deposition current density of 20 mA cm⁻² or higher. However, vigorous stirring of the bath enabled the deposition at a current density of 20 mA cm⁻² or higher, along with a significant increase in coating thickness. On the other hand, roughness of the coating increased at higher stirring speeds. X-ray diffraction measurement showed 26% increase in normalised intensity of (111) reflection on increasing the stirring speed up to 800 rev min⁻¹, whereas the intensity of (200) reflection was found to be decreased by 37%. Scanning electron microscopy and energy dispersive X-ray analysis of the anodised aluminium showed formation of less porous aluminium oxide film.