Electrodeposition of Aluminum–Tungsten Alloy Films Using EMIC-AlCl₃-W₆Cl₁₂ Ionic Liquids of Different Compositions

Abstract

Electrodeposition of Al–W alloy films with high W contents has been carried out using 1-ethyl-3-methylimidazolium chloride (EMIC)–aluminum chloride (AlCl₃) ionic liquids containing tungsten(II) chloride (W₆Cl₁₂). Although the corrosion resistance and hardness of the alloy films are expected to be improved with an increase in the W content, dense films with W contents higher than ∼12 at% have not been obtained by electrodeposition to date. This study has demonstrated that electrodeposition using a EMIC-AlCl₃-W₆Cl₁₂ bath with a lower AlCl₃/EMIC molar ratio can yield Al–W alloys with higher W contents. The maximum W content of the alloys electrodeposited using the EMIC–1.5AlCl₃ bath reached 19.4 at%. The alloy films with up to ∼18 at% W were dense and smooth, whereas those with >∼18 at% W exhibited increased surface roughness. The hardness and Young’s modulus of the dense and smooth 17.7 at% W film were determined by nano-indentation. The hardness of this film was confirmed to be higher than those of the Al–W alloy films previously obtained from the EMIC–2AlCl₃ baths.