Combinatorial corrosion study of the passivation of aluminium copper alloys

An Al_96.1–Cu_3.9 to Al_51.4–Cu_48.6 material library was obtained by thermal co-deposition and characterized by EDX and XRD. The crystallographic data reveals the presence of Al₂Cu and pure aluminium depending on the film composition and following the stoichiometry. Utilizing a scanning droplet cell setup, the zero current potential for anodization, the oxide formation factor and the dielectric constant of the oxide formed are presented with high resolution along the composition gradient.While the dielectric constant of the oxide formed remains nearly unaffected by the increasing copper content of the base material along the composition gradient, the zero current potential shows well defined steps between 6.9 and 8.5 at.% as well as between 20.9 and 26.7 at.% copper indicating an increased thickness of the native oxide present on the film. Additionally, starting around 25 at.% copper, oxygen evolution gradually superimposes the oxide growth and in turn significantly reduces the current efficiency for anodization. The formation of the intermetallic phase Al₂Cu was linked to both phenomena as it promotes the growth of native oxides and current leakage by oxygen evolution.