Al-Zn codeposition on an AZ91D magnesium alloy from a Lewis acidic aluminum chloride-1-ethyl-3-methykimidazolium chloride ͑AlCl 3 -EMIC͒ ionic liquid containing various contents of ZnCl 2 has been successfully established. The experimental results showed that the amount of Zn in the deposit increased with increasing concentration of ZnCl 2 in the electrolyte but decreased with increasing magnitude of cathodic potential. The presence of Zn in the deposit could cause a decrease in surface roughness as compared with that of plain Al deposit. The results of polarization curve measurement showed that Al and Al-Zn coatings could improve the passivation behavior of the AZ91D magnesium alloy in 3.5 wt % NaCl solutions.Magnesium and its alloys have a high specific strength and become one of the most promising metallic materials for use in structural components. However, they are active and have poor corrosion resistance even in mild corrosive environments. 1,2 Thus, to expand their applications, surface treatments such as anodization, 3,4 electroless nickel plating, 5 and organic coating, 6 etc. are frequently applied to the components made of magnesium alloys. A previous study has proven that electrodeposition of Al on magnesium alloy surface could be achieved by employing acidic aluminum chloride-1-ethyl-3-methylimidazolium chloride ionic liquids ͑AlCl 3 -EMIC͒ as the electrolyte. 7,8 The electrodeposition of Zn onto Mg alloys from air and water stable ionic liquids has also been reported. 9 Though codeposition of Al with other metallic elements from ionic liquids has been explored, 10-12 none has been applied on the surface of Mg or its alloys. Concerning the chemical compatibility between the coating and the substrate, codeposition of Al and Zn on the surface of magnesium alloy such as AZ91D is of interest and has practical importance. Thus, in this investigation, the codeposition of Al and Zn from an AlCl 3 -EMIC ionic liquid with the addition of various concentrations of ZnCl 2 was explored. The corrosion and electrochemical behavior of the deposited film were also characterized. ExperimentalAn acidic ionic liquid with an AlCl 3 to EMIC molar ratio of 60:40 was prepared by slow addition of a certain weight of AlCl 3 into EMIC at room temperature. For brevity, the AlCl 3 -EMIC consisting of 60% molar fraction of AlCl 3 is denoted as 60 m/o AlCl 3 -EMIC in this article. The additive, 0.5 or 1 wt % of anhydrous ZnCl 2 , was dissolved directly in the 60 m/o AlCl 3 -EMIC to prepare the codeposition plating bath.A die-cast AZ91D magnesium alloy with a chemical composition of 9.02 wt % Al, 0.49 wt % Zn, and balanced magnesium was used as the substrate. A three-electrode system was used for electroplating in a glove box. The magnesium alloy was assembled as the working electrode, while an Al wire placed in a separated fritted glass tube containing the 60 m/o AlCl 3 -EMIC was used as the reference electrode. The counter electrode was Al ͑for pure Al deposition͒ or Zn ͑for Al-Zn codeposition͒ spiral, which was directly immers...

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The electrochemical behaviors of various metals with and without diamond-like-carbon (DLC) coating in 3.5 wt% NaCl solution were investigated. The effect of hydrodynamic conditions was focused by employing a rotating disc electrode (RDE). The experimental results showed that each bare metal had a more positive corrosion potential and a higher corrosion rate due to enhanced oxygen transport at the higher rotating speed of the RDE. DLC coating caused a substantial increase in the corrosion resistance of all metals studied. However, localized corrosion was still found in the DLC-coated metal at sites where deposition defects existed. Surface morphology examination was performed after the electrochemical test to confirm the roles of hydrodynamic conditions and DLC coating.

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