Electrodeposition of Al–Zn on Magnesium Alloy from ZnCl[sub 2]-Containing Ionic Liquids

Abstract

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...

Ternary alloying additions and multilayering as strategies to enhance the galvanic protection ability of Al-Zn coatings electrodeposited from ionic liquid solution

“…The electrodeposits from 6 to 10 mA/cm 2 had a bright silver surface appearance, while the lower current density deposits had duller surfaces ranging from light gray at 4.8 mA/cm 2 to dark gray at 2.4 mA/cm 2 . Particularly at lower current densities, the Al-Zn electrodeposits exhibit a dual-phase microstructure, with zinc dendrites embedded in an aluminum-rich matrix, quite similar to the microstructures reported by Pan et al [15,16]. As shown in Fig.…”

“…One promising alternative approach to electrodeposition of aluminum-zinc multilayers is through use of room temperature ionic liquids. In particular, ionic liquids consisting of a mixture of AlCl 3 and 1-ethyl-3-methylimidazolium chloride (EMIC) have been successfully used to electrodeposit pure aluminum [10][11][12][13][14] as well as a wide range of aluminum alloys, including Al-Zn [15,16], Al-Mn [17][18][19][20][21][22][23][24], Al-Zr [25], and many others [26][27][28][29][30][31][32][33][34][35][36][37]. In Al-Mn, there is even prior work reporting multilayered coatings, in which the composition and microstructure were controlled between layers through modulation of deposition current density [23,24].…”

“…In Al-Mn, there is even prior work reporting multilayered coatings, in which the composition and microstructure were controlled between layers through modulation of deposition current density [23,24]. Pan et al [15,16] reported successful electrodeposition of Al-Zn from AlCl3-EMIC mixtures with 1 wt.% ZnCl2, with compositions ranging from approximately 20 to 100 at.% Zn, depending on the deposition voltage. However, formation of zinc dendrites was observed in the high zinc coatings, leading to a very rough surface and inhomogeneous composition.…”

Cold sprayed aluminum based glassy coating: Synthesis, wear and corrosion properties

“…Al-based nanocrystalline and glassy coatings have been synthesized by electrodeposition method [33][34][35][36][37][38]. However, electrodeposition restricts coatings on large engineering components due to bath size limitation.…”

Investigation of Al-Ni Alloys Deposition during Over-discharge Reaction of Na-NiCl2Battery

“…For this reason, electro-deposition has been studied as an alternative method to form Al alloy successfully. [11][12][13] Although it is well known that Al could be formed in Zebra battery cells, there is no reports treating Al deposition in the cathode current collectors of Zebra battery even without cell failure. Interestingly, Al-Ni alloy codeposition was reported to occur in the NiCl 2 / AlCl 3 /EMImBr (0.03/2/1) solution at 0.3 V higher voltage 14) than that of pure Al deposition.…”