Electrodeposition of Zinc-Magnesium alloy from 1-Ethyl-3-Methylimidazorium Bromide Molten Salt

Abstract

The electrodepositon of Zn-Mg alloys was tried by potentiostatic electrolysis and cathodic polarization in Lewis basic 1-ethyl-3-methylimidazorium bromide (EMIB)-ZnBr₂-MgBr₂-ethylene glycol molten salts at 120°C. The molten salts used were prepared by chemical displacement of prescribed amounts of Zn in EMIB-ZnBr₂-EG molten salts by Mg. The cathodic polariozation curves showed that EMI⁻ cation in the molten salt decomposed below −0.8 V (vs. Zn/EMIB-ZnBr₂-EG (45 : 10 : 45 mol%)). Thus the potentiosatatic electrolysis was carried out at −0.6 V and grayish metallic-colored electrodeposits were obtained. The X-ray diffraction analysis showed the diffraction lines of Mg₂Zn₁₁ in addition to Zn, CuZn₅ and the substrate Cu. This result indicates the Zn-Mg alloy plating can be done by using EMIB-ZnBr₂-MgBr₂-EG molten salts. The Mg content in the electrodeposit obtained from the EMIB-ZnBr₂-MgBr₂-EG (18 : 6 : 4 : 72 mol%) molten salt was 2.5 mol%. Corrosion resistance of Zn-2.5 mol% Mg alloy coating steel was about 13 times compare with that of Zn coating steel in the 5 mass% NaCl aqueous solution at 35 °C.