Fast electrochemical deposition of corrosion resistant mixed hydroxide films from Zn/Al-nitrate aqueous electrolytes on zinc coated steel

Corrosion resistant amorphous mixed zinc/aluminium (oxy)hydroxide films were electrodeposited on zinc coated steel from aqueous solutions containing sodium nitrate, zinc nitrate and aluminium nitrate. The ratio of Zn 2+ and Al 3+ in the solution was 5:2. Homogeneous films were cathodically deposited within 10 s. The resulting microstructure of the films was analyzed by means of field-emission scanning electron microscopy (FE-SEM). The film deposition rate was estimated by determination of the cross-sectional film thickness to be about 0.5 nm/s. The deposition mechanism was revealed based on the film composition, which was characterized by means of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and time-dependent Fourier transform infrared reflection-absorption spectroscopy (FT-IRRAS) measurements. The formation of a predominantly amorphous aluminium (oxy)hydroxide enriched film was observed. Electrochemical corrosion analysis by electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV) showed that the deposited films led to a significant inhibition of both cathodic and anodic corrosion reactions already at deposition time of 10 s corresponding to a film thickness of about 5 nm. • Fast electrodeposition of mixed hydroxide films from aqueous solution • The amorphous Zn/Al film is enriched in aluminium (oxy)hydroxides. • Mixed hydroxide films lead to corrosion protection of the zinc coating.