Zn–Ni alloys having compositions in the range 14–18 wt-% are electrodeposited using direct current DC and pulse current PC in a cyanide-free alkaline electrolyte. Homogeneous and compact layers, suitable for corrosion protection, are obtained. Contrary to the common acceptance, X-ray diffraction spectra and differential scanning calorimetry thermal analysis show that the electrodeposited c alloy by DC plating in electrolytes with complexant-additive agents has to be regarded as a metastable phase, whose atomic arrangement is different from that of the equilibrium c intermetallic compound. A model for atomic distribution and the Gibbs free-energy function for the DC electrodeposited phase are discussed. It is found that PC deposited alloys from additive-free electrolytes present the same metastable behaviour attributed to the DC plated homologues in electrolytes with complexant-additive agents. The corrosion behaviour is found to be dependent on the duty cycle applied during PC deposition, as evidence of the different microstructures obtained in varying the parameters.

Direct and pulse plating of metastable Zn-Ni alloys

IEFFA, SIMONA;BERNASCONI, ROBERTO;NOBILI, LUCA GIAMPAOLO;CAVALLOTTI, PIETRO LUIGI;MAGAGNIN, LUCA
2014

Abstract

Zn–Ni alloys having compositions in the range 14–18 wt-% are electrodeposited using direct current DC and pulse current PC in a cyanide-free alkaline electrolyte. Homogeneous and compact layers, suitable for corrosion protection, are obtained. Contrary to the common acceptance, X-ray diffraction spectra and differential scanning calorimetry thermal analysis show that the electrodeposited c alloy by DC plating in electrolytes with complexant-additive agents has to be regarded as a metastable phase, whose atomic arrangement is different from that of the equilibrium c intermetallic compound. A model for atomic distribution and the Gibbs free-energy function for the DC electrodeposited phase are discussed. It is found that PC deposited alloys from additive-free electrolytes present the same metastable behaviour attributed to the DC plated homologues in electrolytes with complexant-additive agents. The corrosion behaviour is found to be dependent on the duty cycle applied during PC deposition, as evidence of the different microstructures obtained in varying the parameters.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11311/962655
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