Zinc-nickel Alloy Research Articles

Zinc-Nickel alloy coatings electrodeposited by pulse current and their corrosion behavior

Steel in subtropical monsoon regions encounters severe atmospheric corrosion. In an attempt to provide better corrosion protection, zinc-nickel alloys were electrodeposited on steel by pulse current. Some electric variables (average current density and pulse cycle) and bath temperature on chemical compositions and grain size of coatings were studied. Next, zincnickel alloys electrodeposited on steel were prepared for atmospheric corrosion tests. In addition, the determination of the chemical compositions and the grain size of the Zn-Ni alloy coatings were conducted by scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDS) and scanning probe atomic force microscope (AFM). Furthermore, Tafel plots were employed to evaluate the alloy corrosion behavior.

Electrodeposition of Zn–Ni alloys from sulfate bath

The electrodeposition of zinc–nickel (Zn–Ni) alloys from sulfate baths has been studied at different deposition times and H2SO4 and NiSO4 concentrations; various characteristics have been observed during alloy deposition and dissolution. The deposit has been investigated by using scanning electron microscopy (SEM) and X-ray diffractometry. Cyclic voltammetry and galvanostatic measurements during electrodeposition have been conducted. Electrochemical and surface analysis indicate that deposition takes place with the formation of two different structures corresponding to γ-phase and δ-phase zinc–nickel alloys. During anodic part of the cyclic voltammetry of the alloys, a reduction process has been observed, which may be due to hydrogen evolution. With the increase of nickel concentration in the bath, the amount of γ-phase increases, as indicated by the relative increase in the height of the peaks in the X-ray patterns and anodic peaks in the cyclic voltammograms. Also, the corrosion resistance of the zinc–nickel alloy has been improved with an increased concentration of nickel. Under these experimental conditions the electrodeposition of the alloys is of anomalous type.

A study on electroplating of zinc nickel alloy with HEDP plating bath

The electroplating of bright Zn-Ni alloy process using HEDP as coordinating agent, ZNP as additive agent is studied. The effect of coordinating agent, chloride content, [Zn2+]/[Ni2+], cathode current density, temperature, and supplementary coordinating agent on Ni content is investigated; composition and physical phase of alloy plating layer, brightness of plating layer, and stability of plating solution are comprehensive considered; and also, the optimum composition of plating solution for bright Zn-Ni alloy electroplating and technological condition is determined; finally, deposition mechanism is discussed.

Selective electrodeposition of zinc–nickel alloy through porous medium

The ‘portable electrodeposition’ method described in this work differs from the conventional brush plating method in that it utilizes a reservoir that contains the electrolyte. A diffusion medium allows the cations to migrate to the working electrode surface (cathode) in continuous mode such that the coating is made selectively in the region, which comes in direct contact with the diffusion medium. The diffusion medium also prevents the working surface from being flooded with the electrolyte and dispenses the electrolyte in a more controlled fashion. Unlike conventional flow plating, this prevents the spillage of the electrolyte solution reducing environmental pollution and comparatively requires lower wattage power supply. To characterize the results of the above technique, zinc–nickel alloy coatings were made at different potentials using various types of diffusion media. The coatings were tested for chemical composition, galvanic protection, hardness, and porosity.

Effects of Electroplated Zinc-Nickel Alloy Coatings on the Fatigue Strength of AISI 4340 High-Strength Steel

Recovered substrates have been extensively used in the aerospace field. Cadmium electroplating has been widely applied to promote protective coatings in aeronautical components, resulting in excellent corrosion protection combined with a good performance in cyclic loading. Ecological considerations allied to the increasing demands for corrosion resistance have resulted in the search for possible alternatives. Zinc-nickel (Zn-Ni) alloys have received considerable interest recently, because these coatings show advantages such as a good resistance to white and red rust, high plating rates, and acceptance in the market. In this study, the effect of electroplated Zn-Ni coatings on AISI 4340 high-strength steel was analyzed for rotating bending fatigue strength, corrosion, and adhesion resistance. The compressive residual stress field was measured by x-ray diffraction prior to fatigue tests. Optical microscopy documented coating thickness, adhesion characteristics, and coverage extent for nearly all substrates. Fractured fatigue specimens were investigated using scanning electron microscopy (SEM). Three different Zn-Ni coating thicknesses were tested, and comparisons with the rotating bending fatigue data from electroplated Cd specimens were performed. Experimental results differentiated the effects of the various coatings on the AISI 4340 steel behavior when submitted to fatigue testing and the influence of coating thickness on the fatigue strength.

Electrochemical deposition and characterization of zinc-nickel alloys deposited by direct and reverse current

Zn-Ni alloys electrochemically deposited on steel under various deposition conditions were investigated. The alloys were deposited on a rotating disc electrode and on a steel panel from chloride solutions by direct and reverse current. The influence of reverse plating variables (cathodic and anodic current densities and their time duration) on the composition, phase structure and corrosion properties were investigated. The chemical content and phase composition affect the anticorrosive properties of Zn-Ni alloys during exposure to a corrosive agent (3%NaCl solution). It was shown that the Zn-Ni alloy electrodeposited by reverse current with a full period T = 1 s and r=0.2 exhibits the best corrosion properties of all the investigated alloys deposited by reverse current.

Investigation of nanocrystalline zinc–nickel alloy coatings in an alkaline zincate bath

Nanocrystalline zinc–nickel alloy coatings obtained from an alkaline zincate bath containing a laboratory-made additive were investigated in this paper. The effects of the additive content and the cathode current density on the grain sizes of the coatings were studied. SEM and TEM observations and XRD analysis were performed to examine the microstructure (grain size) and phase composition of the coatings. The experimental results indicated that the addition of the additive leads to a much brighter and a more uniform nanocrystalline deposition with the grain sizes varying from 14 to 33 nm. The Hull cell test was used to determine the optimum ranges of both the cathode current density and the additive content. Salt spray tests and polarization measurements indicated that the nanocrystalline zinc–nickel alloy coatings have a better corrosion resistance than the zinc coatings deposited from a simple alkaline zincate bath.

The Structure and Texture Development of Ni Alloy Electrodeposits—III Nickel-Zinc Electrodeposits

SUMMARYElectrodeposited nickel-zinc alloys have been studied using ‘direct’ methods e.g. x-ray diffraction and transmission electron microscopy on coatings having different thicknesses, deposited on mild steel and copper substrates at current densities of 10 and 60 mA cm2. In all cases the coatings evolved with a complex bcc gamma phase. The work has confirmed and extended the ideas of Finch et al.1 3 and Pangarov4-6 to alloy deposition. It has been shown that a better understanding, particularly of the initial deposition stages, can be obtained by considering both strain and surface energy effects. In all cases the film formed at the coating/substrate interface develops with a {110} texture on both mild steel and copper substrates at current densities of 10 and 60 mA cm2. From surface energy considerations a {110} texture would be expected as in bcc metals this orientation has the lowest surface energy. XRD measurements by glancing angle indicate that in the initial stage of deposition, the zinc and nickel atoms deposit in the recesses in the {110) plane of the mild steel as the initially formed deposit had a d-spacing similar to that of the mild steel. Similar effects were also indicated for the nickel-zinc film deposited on copper substrates indicating that ‘templating’ occurs during deposition on both mild steel and copper substrates. A semi-quantitative model based on surface energy and strain energy considerations has been used to explain the texture development. Furthermore, the structures of deposits studied in the present work tended to be fine grained in the initial stages but developed coarser columnar due to selected grain growth with favoured grains becoming broader during the intermediate and final of growth. However, unlike previous work on bcc nickel-zinc alloys7 which developed a {111} texture in thicker films the {110} texture remained dominant in the majority of the films examined and the final texture in 20 μm bulk films was a {110}.

Electrochemically Deposited Zinc-Nickel Alloys

The mechanism of formation of a zinc-nickel alloy under the conditions of normal and anomalous electrochemical codeposition (accompanied by enrichment of the deposit with nickel or zinc) were studied. The manner in which the composition, structure, and properties of the zinc-nickel alloy vary with the electrolyte composition (nature of ligands and molar ratio of codeposited metals) and deposition conditions (potential and current density) was determined.

Study of the corrosion properties of zinc–nickel alloy electrodeposits before and after chromating

In this study, corrosion behavior of zinc–nickel alloy electrodeposits on steel sheets has been investigated using the neutral salt spray test. The performance of the coatings with various nickel contents (up to 28 wt.%) was compared with electrodeposited zinc coating. The results show that the corrosion resistance of zinc–nickel alloy coatings is superior to that of pure zinc coating and the zinc–13 wt.% nickel gives the best protection. The corrosion behavior of chromated zinc–nickel alloy coatings was also studied. The results show that chromate conversion coating increases the corrosion resistance significantly (up to 3–4 times), and the best corrosion resistance is achieved by chromating of zinc–13 wt.% nickel alloy coating.

Sliding wear behaviour of Zinc–Nickel alloy electrodeposits

The sliding wear behaviour of zinc–nickel electrodeposited coatings on mild steel substrates was investigated using a spherical pin-on-disc apparatus. The pin materials were alumina and hardened steel. The composition of the coatings was the following: 86 wt% zinc–14 wt% nickel. The friction coefficient of zinc–nickel coating against alumina counter spheres was found to be higher than that against hardened steel counter spheres. The weight loss of zinc–nickel coating after sliding against hardened steel counter spheres was found to be lower than that against alumina counter spheres. The main wear mechanism of the zinc–nickel coating sliding against stainless steel was noted to be severe shearing of the surface layers of the coating due to the ploughing action of the steel pins. For the wear experiments of zinc–nickel coatings against alumina spheres, a surface delamination mechanism is proposed to be the predominant wear mechanism of the coatings.

Heat-Treatment on Black-Passivated ZnNi Alloys

Zinc-nickel alloys obtained from an alkaline bath were passivated with a black, silver-free, chromate conversion coating (CCC). The attack of the chromate solution on the coatings changed most of their characteristics. The CCC modified the composition, thickness, structure, roughness, and stress level of the alloys. Since most of the accelerated corrosion tests include a heat-treatment prior to the measurements, the chromated coatings were subjected to this treatment and their characteristics were evaluated again. We observed that while most of the coating properties were unaffected by the heat-treatment, the corrosion resistance was improved. Scanning force microscopy was finally used to find the differences that could explain this change in the corrosion behavior of the coatings. © 2003 The Electrochemical Society. All rights reserved.

An EXAFS investigation of molybdate-based conversion coatings

The composition of molybdate-based conversion coatings on zinc–nickel alloy electrodeposits was examined by extended X-ray absorption fine structure (EXAFS). The absorption spectra from appropriate standards showed distinct differences between the Mo(IV) and Mo(VI) oxidation states. A pre-edge peak was apparent for the various molybdate species and molybdenum trioxide, with the energy and intensity dependent on the coordination of the molybdenum. A shift in the molybdenum K-edge spectra was also evident between Mo(IV) and Mo(VI) compounds. A qualitative analysis revealed that both Mo(IV) and Mo(VI) species were present within the molybdate-based conversion coating, with a significant prevalence of hexavalent molybdenum.

The influence of pulse parameters on Zn-Ni alloy coatings plated on AZ91 magnesium alloy

SUMMARYThe influence of pulse parameters on zinc-nickel coatings plated on AZ91 magnesium alloy is investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The particles of zinc-nickel alloy plated on AZ91 magnesium alloy become smaller and the surface roughness decreases with the increase of current density and frequency. However, long plating times and a high ratio of ton/toff have decremental effects on the particles and surface roughness. The contents of crystal phases of zinc-nickel alloy coatings are higher under pulse current deposition than under direct current. The frequency, current density, plating time and ratio of ton/toff have different impacts on the thickness and Ni content of zinc-nickel coatings.

Residual Stress and Other Structural Characteristics of Electroplated ZnNi Alloys

Zinc-nickel alloys obtained from a new alkaline electrolyte were characterized by analyzing their composition, morphology, structural parameters, and residual stress. The influence of various deposition parameters, such as current density, plating temperature, or deposit thickness, on these coating characteristics was analyzed. The results indicated that the alloys maintained their characteristics in a wide range of deposition conditions: they were uniform in appearance, consisted of almost pure γ phase, and had a tensile stress lower than that measured for other Zn-Ni alloys of similar composition obtained from other electrolytes. © 2002 The Electrochemical Society. All rights reserved.

Anodic Dissolution of Ni50Zn Alloy in the Presence of Mixtures of Organic Additives with Sodium Chloride

Electrochemical behavior of nickel and nickel-zinc alloy in an acidic perchlorate media was studied as influenced by some organic additives, sodium chloride, and their binary mixtures.

On the zinc-nickel alloy electrodeposition mechanism

It is shown that during the zinc–nickel alloy electrodeposition in sulfate–chloride electrolytes, the predominant zinc deposition into the alloy can be caused by the generation of a film in the cathode diffusion layer formed of highly-disperse colloid zinc compounds.

Electrochemical deposition and characterization of zinc-nickel alloys deposited by direct and pulse current

Chemical composition and phase structure of Zn-Ni alloys obtained by electrochemical deposition under various conditions were investigated. The alloys were deposited on a rotating disc electrode and steel panel from chloride solutions by direct and pulse current. The influence of the pulse plating variables (on-time, off-time, relation of off- and on-time) on the composition, phase structure and corrosion properties were investigated. The phase composition affects the anticorrosive properties of Zn-Ni alloys during exposure to a corrosive agent (3% NaCl solution). It was shown that a Zn-Ni alloy electrodeposited by pulse current with a pulse time of 1 ms and an off- and on-time ratio of 1 exhibits the best corrosion properties.

Complexing agents for a Zn–Ni alkaline bath

Zinc–nickel alloys were obtained from alkaline electrolytes. Four amines, all of which are good complexing agents for nickel, were tested to identify their effects on the deposition process and final plate. The influence of THEED, an additive commonly used with alkaline electrolytes, was also examined. The electrochemical analysis showed some differences between acid and alkaline deposition processes, but no great influence was observed for the amine type. All four amines gave a consistent nickel content throughout the range of currents tested. The main difference was obtained in the structure of the alloys since some of the coatings showed an η-phase with an unusually high Ni content.

Zinc–nickel alloy electrodeposits for water electrolysis

Electrodeposited zinc–nickel alloys of various compositions were prepared. A suitable electrolyte and conditions to produce alloys of various compositions were identified. Alloys produced on electroformed nickel foils were etched in caustic to leach out zinc and to produce the Raney type, porous electro catalytic surface for hydrogen evolution. The electrodes were examined by polarization measurements, to evaluate their Tafel parameters, cyclic voltammetry, to test the change in surface properties on repeated cycling, scanning electron microscopy to identify their microstructure and X-ray diffraction. The catalytic activity as well as the life of the electrode produced from 50% zinc alloy was found to be better than others.