Electrodeposition of Al-W alloy films in a 1-ethyl-3-methyl-imidazolium chloride-AlCl₃ ionic liquid containing W₆Cl₁₂

Abstract

The electrodeposition of Al-W alloy films in a Lewis acidic 1-ethyl-3-methyl-imidazolium chloride (EMIC)-AlCl₃ ionic liquid using W₆Cl₁₂ as the W ion source was investigated. W₆Cl₁₂ dissolved in the ionic liquid at a higher concentration than other W ion sources used in previous studies. Potentiostatic electrodeposition was performed in a bath containing W₆Cl₁₂ at a concentration of 49 mM. Dense Al-W alloy films containing up to 12 at.% W were electrodeposited at potentials more negative than 0 V vs. Al/Al(III). The deposition current density at >0 V was lower than 0.3 mA cm⁻², while that for Al-W alloy films was higher and reached 38 mA cm⁻² at -0.5 V. The deposition of W was induced by the deposition of Al. At lower W concentrations, the Al-W alloy films were composed of a super-saturated solid solution, and in the W content range of 9-12 at.% they comprised an amorphous phase. Potentiodynamic polarization and nano-indentation showed that the Al-W alloy films containing 10-12 at.% W exhibited high pitting corrosion resistance, high hardness, and low Young's modulus.