Electrodeposition of Al coating on Mg alloy from Al chloride/1-ethyl-3-methylimidazolium chloride ionic liquids with different Lewis acidity

摘要

Electrodeposition of a metallic Al layer on a Mg alloy from a Lewis acidic Al chloride-1-ethyl-3-methylimidazolium chloride (EMIC) ionic liquid has been carried out at room temperature. The effects of the AlCl3 to EMIC molar ratio, in the range from 50%-50% to 60%-40%, on the electrodeposition characteristics were investigated. Scanning electron microscopy, X-ray energy dispersive spectroscopy, and X-ray diffractometry were used to examine the surface morphology, the chemical composition, and the crystal structure of the deposited layers prepared in the ionic liquids with different AlCl{sub}3 to EMIC ratios. The improvement of corrosion resistance of a Mg alloy to the Al surface coating was also evaluated by means of various electrochemical methods. The electrochemical impedance spectroscopic data indicated that while a bare Mg alloy had a polarisation resistance of only 470 Ω cm{sup}2 in 3·5 wt-% NaCl solution, the Al coated sample deposited in the ionic liquid with 60% AlCl{sub}3 showed a resistance as high as 5200Ωcm{sup}2 in the same environment.