Abstract :
[en] An additive-free gluconate based alkaline electrolyte was used to study the electrodeposition of Zn and Zn-Fe
coatings. Cyclic voltammetry was performed to define the accurate deposition parameters and to identify the
reactions taking place. Electrodeposition was performed using direct and pulse currents. Electrodeposits were
characterized in terms of morphology, microstructure, mechanical and corrosion properties. Homogeneous Zn
and Zn-Fe 7 wt% Fe were obtained, composed of hexagonal and blunted pyramidal grains respectively. Pulse
current deposition was carried out to improve the morphology and to reduce the impact of hydrogen evolution
reaction. Deposition parameters such as on-time/off-time/peak current density (ton/toff/jp) were investigated.
The average current density jm seems to control the composition of Zn-Fe electrodeposits. High iron contents
were obtained at low current densities and the iron content abruptly decreased when the current density
increased for both direct and pulse currents electrodeposition. Incorporation of iron led to an increase of the
micro-hardness of the coating. Scratch tests were performed in order to evaluate the damage of the coatings, and
the coating adhesion could be assessed. Polarization curves in 3.5 wt% NaCl after 1 h of immersion at the open
circuit potential did not show any change of corrosion potential between Zn and Zn-Fe 7 wt% Fe deposits. This
potential was shifted to a more positive value for Zn-Fe 14 wt% Fe, which points out this coating as the best
choice to reduce the galvanic corrosion between the steel substrate and the Zn-Fe deposit. These results were
linked to the microstructure of the deposits and perhaps to the presence of Γ1-Fe5Zn21 phase for Zn-Fe 14 wt%
Fe.
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