A Concentrated AlCl₃–Diglyme Electrolyte for Hard and Corrosion-Resistant Aluminum Electrodeposits

A concentrated aluminum chloride (AlCl₃)-diglyme (G2) electrolyte is used to prepare hard and corrosion-resistant aluminum (Al) electrodeposited films. The Al electrodeposits obtained from the electrolyte with an AlCl₃/G2 molar ratio x = 0.4 showed a void-free microstructure composed of spherical particles, in stark contrast to flake-like morphologies with micro-voids for lower x. Neutral complexes rarely exist in the x = 0.4 electrolyte, resulting in a relatively high conductivity despite the high concentration and high viscosity. Nanoindentation measurements for the Al deposits with >99% purity revealed that the nanohardness was 2.86 GPa, three times higher than that for Al materials produced through electrodeposition from a well-known ionic liquid bath or through severe plastic deformation. Additionally, the void-free Al deposits had a <100> preferential crystal orientation, which accounted for better resistance to free corrosion and pitting corrosion. Discussions about the compact microstructure and <100> crystal orientation of deposits obtained only from the x = 0.4 concentrated electrolyte are also presented.