Direct and pulse plating of metastable Zn–Ni alloys. (November 2014)

• Record Type: Journal Article
• Authors: Ieffa, S.; Bernasconi, R.; Nobili, L.; Cavallotti, P. L.; Magagnin, L.
• Is Part Of: Transactions of the Institute of Metal Finishing. Volume 92:Number 6(2014:Nov.)
• Page Start: 321
• Page End: 324
• Publication Date: 2014-11
• Subjects: Zinc, -- Nickel, -- γ phase, -- Reverse pulse current, -- Corrosion; Metals -- Finishing -- Periodicals; Metals -- Surfaces -- Periodicals; Metallurgy -- Periodicals; 671.705
• DOI: 10.1179/0020296714Z.000000000209
• Languages: English
• ISSNs: 0020-2967

Abstract

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 γ 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 γ 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.