Zn-Fe Coatings Research Articles

Effect of applied magnetic field on ZnFe alloy electrodeposition

Corrosion-resistant materials for the protection of structures are of paramount importance to the industry. This research work reports on the effects of a magnetic field applied parallel to a working electrode on the electrodeposition process of the corrosion-resistant ZnFe alloy coating. The electrochemical study of ZnFe alloy coatings prepared using an acid sulfate bath was carried out in galvanostatic mode. The results indicated that the current density and magnetic field have remarkable effects on the formation kinetics of the ZnFe deposits. The diffusion rate of the Fe ferromagnetic species subjected to mass transport accelerated under the influence of the Lorentz force (applied magnetic field); moreover, these ions were deposited in large amounts under the effect of the magnetic field. The energy-dispersive X-ray (EDX) spectroscopy analysis confirmed the modification of the Fe ion atomic concentrations in the ZnFe coatings under the influence of the magneto-hydrodynamic (MHD) convection compared to those deposited without the imposition of the magnetic field. The morphological examinations revealed that the magnetic field acted positively on the deposited layers by endowing them with homogeneous surfaces. The X-ray diffraction (XRD) analysis of ZnFe deposits demonstrated the presence of delta (δ), zeta (ξ) and eta (η) phases when there was no applied magnetic field. Furthermore, depending on the magnitude of the applied magnetic field, XRD diagrams exhibited changes in crystallographic orientation, grain size, and the electro-crystallization. These changes favor the presence of certain crystallographic phases, such as (200) and (330).

Fabrication of biodegradable superhydrophobic Zn-Fe coating on ultra-light Mg-Li alloy

As a typical biodegradable and biocompatible light metal, magnesium (Mg) and its alloys exhibit significant prospects for various applications, especially in biomedical materials. Unfortunately, their actual application fields have been restricted by too fast degradation/corrosion rate. Both zinc (Zn) and iron (Fe) are biodegradable and biocompatible but stabler thermodynamically. It's one of the considerable refreshing strategies for controlling the degradation rate of Mg substrate by constructing a ZnFe coating with superhydrophobicity on it. However, it's challenging and rarely reported due to the high chemical reactivity of Mg. This study reports the successful in-situ synthesis of ZnFe coatings with hierarchical micro-/nano-scale structures and superhydrophobicity on ultra-light MgLi alloy by employing an innovative weak alkaline aqueous bath followed by simple chemical modification. Their micromorphology, chemical and phase compositions as well as surface wettability were comprehensively analyzed by FE-SEM, EDS, XRD, XPS, FT-IR, and a contact angle measuring instrument. Furthermore, the degradation behavior of the typical samples was evaluated by modern electrochemical measurement technology. The results revealed that the coating comprised dense micro-papillary structures and nanosheets, exhibiting a static contact angle of droplets up to 161.5° and a sliding angle of 3.0°. In addition, the obtained sample demonstrated a significantly reduced degradation rate compared to the bare magnesium alloy.

Structural Properties of Zn-Fe Alloy Coatings and Their Corrosion Resistance

Single-layer and multilayer alloy deposits were coated onto a mild steel substrate by a single-bath electroplating process. The developed coating consists of Zn and Fe alloys having different compositions with different layers. The anticorrosion behavior of single-layer and multilayer deposits was evaluated by the potentiodynamic polarization method. The surface morphology of the deposits was studied with a scanning electron microscope. The crystal structure of the deposits was analyzed with the X-ray diffraction technique. The Fe content in the deposit was analyzed by a colorimeter and verified with energy-dispersive X-ray spectroscopy. The micro-hardness tester with a Vickers indenter was used to evaluate the microhardness of the developed single-layer and multilayer coatings. It was found that the microhardness increased with applied current densities. The Zn-Fe multilayer coatings with 300 layers deposited with square and triangular pulses at the applied current density of 2.0/3.0 A dm−2 were five and four times more corrosion-resistant, respectively, than the single-layer coating of the same thickness. The development of Zn-Fe coatings that are resistant to corrosion is particularly important for the automotive industry and steel-based vehicle parts.

Influence of Friction on the Formability of Fe-Zn-Coated IF Steels for Car Body Parts

This paper presents the formability results of galvanized Zn-Fe-based interstitial-free (IF) “galvanneal” steel sheets with different degrees of alloying. The Fe content of the Zn-Fe coatings was determined by titration method and the phase composition of the coatings was determined by raster electron microscopy with EDX analyzer. A deterioration of the adhesion of the Fe-Zn coating to the substrate was observed in the pre-alloyed coating. The applied modes of annealing and smooth rolling after the surface galvanization resulted in a change in the surface microgeometry parameters Ra and Pc. The suitability of the surface microgeometry of the used Zn-Fe-coated sheets was assessed using control diagrams and the capability indexes Cpk with respect to the defined specifications. The coefficient of friction was determined by dry friction cup test, and using Anticorit lubricant and microtene film as lubricants. With increasing Fe content in the coating, a slight increase in friction coefficient values was observed—a slight deterioration in formability. The results obtained indicate that for car body surface parts, the Fe content of the Zn-Fe coating should range from 7% to 12%.

Relation between Faradic Yields, Hydrogen Evolution and Pulsed Currents: Morphological and Fe Content Control in Zn and ZnFe Coatings

Long-term protection of metallic parts from atmospheric exposure is an important challenge and one of the most frequent way to ensure their corrosion resistance is the application of sacrificial zinc alloys coatings [1]. Among the various zinc electroplating baths, the alkaline zincate solutions has gained a wide range of applications thanks to its simple bath composition, good dispersion and efficient coverage ability. Nevertheless, its efficiency is very low in absence of additives, which affects the performances of the coatings by modifying the crystal growth and therefore the structural and mechanical properties. This is a result from the competition between dihydrogen production and the reduction of the metallic species present in the bath.The present study deals with the optimization of ZnFe sacrificial coating on steel and aluminum substrate in the frame of the ATLAS project -Alternative TechnoLogies for improved Anticorrosion Solutions- managed by the IRT M2P. After the analysis of the electrochemical behavior of the ZnFe electrolyte patented by the Coventya company and the UTINAM institute, pulsed currents will be implemented to extend the versatility of the coatings. Indeed, pulsed currents are known to act on various parameters such as improving the faradic yield or modifying morphologies and structures [2].The determination of a first panel of pulsed sequences (average current densities, cathodic peak current, cathodic pulse time and off-time) have been based on transient curves analysis from a zincate bath. Three sequences have been selected as they resulted in very different patterns in terms of electrochemical behavior and coatings characteristics. These sequences have been replicated and compared to DC current in several electrolytes, from the zincate bath to the commercial formula. For each set of parameters, the faradic yield has been measured and compared to the hydrogen generated during the electrolysis distributed between the absorbed one (measured by hot extraction) and the dihydrogen released into the reactor atmosphere (measured by mass spectrometry with a dedicated set- up). It is interesting to note that the obtained values strongly depend on pulsed sequences as well as electrolytes composition. Coatings were systematically produced and characterized. Morphology was observed using SEM and microstructure determined from XRD diffractograms: preferential orientation and crystal lattice and crystalline phases. The latest has required a specific methodological development.Finally, the identification of nucleation parameters by model simulation has been undertaken to describe the mechanisms involved in the first steps of zinc electrodeposition [3].[1] B. Chatterjee, « Electrodeposition of Zinc Alloys », p. 31.[2] X. Zhang, K. Tsay, J. Fahlman, and W. Qu, « Journal of Energy Storage, 26 p. 100966 (2019)[3] A. Milche, Electrochimica Acta, 48 p.2903-2913 (2003)

Optimization of the morphology, structure and properties of high iron content Zn–Fe coatings by pulse electrodeposition

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.

Zn–Fe and Y-modified Zn–Fe coatings on 42CrMo steel via pack cementation

Zn–Fe and Y-modified Zn–Fe coatings were prepared on 42CrMo steel through pack cementation processes at 370, 390 and 410 °C for 4 h. Y modification was achieved through the co-deposition of Zn and Y2O3. The effects of Y modification on microstructure, formation and corrosion behavior of the Zn–Fe coating were investigated. The coating thickness increased with an increase in temperature. The Y-modified Zn–Fe coating was thicker than the plain Zn–Fe coating. Both the Zn–Fe coating and Y-modified Zn–Fe coating showed single-layered structures, but the overall microstructure was improved by Y modification. The activation energies for Zn–Fe coating and Y-modified Zn–Fe coating were 113.15 and 80.65 kJ·mol−1, respectively. The Zn–Fe coating consisted of FeZn13 and Fe11Zn40 phases. The effects of Y modification on the corrosion behavior of the Zn–Fe coating were evaluated through an immersion test and polarization measurements. The results showed that the corrosion resistance was improved by Y modification.

Effect of Deposition Time on Thickness and Corrosion Behavior of Zn-Fe Coating

Zn-Fe coatings on Q235 steel are prepared by pack cementation process at 390 ◦C for 2, 4, 6, 8 and 10 h to investigate the effects of the deposition time on the thickness and corrosion behavior of the Zn-Fe coatings. The thickness of the coating increases with the increase of the deposition time. The coating is composed of a thick outer layer and a thin inner layer. The formation of the coating depends on the inward diffusion of Zn atoms and the outward diffusion of Fe atoms. The outer layer is composed of Fe11Zn40 and FeZn10 phases. The corrosion behavior of the Zn-Fe coatings is evaluated by immersion test and polarization test. The results show that the Zn-Fe coatings can effectively prevent the Q235 steel from corrosion. The corrosion resistance of the coating is proportional to the deposition time.

Local Mechanical Properties of Zinc-Iron Coated Steel Sheets by Depth-Sensing Indentation

Depth-sensing indentation (DSI) is used in this work to determine the change of local mechanical properties by annealing of hot-dip galvanized IF steel sheets. The influence of annealing conditions (temperature and time) on: (i) coating composition; (ii) local mechanical properties and (iii) roughness of the coating surface was quantified. Annealing of steel samples (Ti-IF steel and Ti-Nb-P-IF steel alloyed with phosphorus) was performed with different holding times (10, 60, and 300 s) by both temperatures 450 and 550 °C. The zinc in coating transformed during annealing to the intermetallic phases ZnxFey. Annealed Zn-Fe coatings, wherein the iron concentration falls towards the surface, consist of different intermetallic phases.

The investigation of K-shell fluorescence parameters of Zn-Fe alloys with different grain size and microstrain values

It is known that zinc alloys with iron group metals have better corrosion resistance than pure zinc. Owing to the corrosion resistance of these alloys, Zn–Fe coatings are widely used in automotive industry and have excellent mechanical performance. In this work, we investigated the relationship between the changes in the measured X-ray fluorescence parameters (Kβ/Kα, σKα and σKβ) and the changes in the structural parameters such as microstrain or grain size values for Zn–Fe alloys that were prepared with different pH values. To explain these changes, the Kα and KβX-ray production cross sections, and the Kβ/KαX-ray intensity ratio values were calculated by three different ways for the elemental forms of Zn and Fe. The structural parameters, such as microstrain and grain size, were also calculated. We expect that the outer shell electronic distribution affects the structural parameters of the produced Zn–Fe alloys, changing the measured Kα and KβX-ray production cross sections, and the Kβ/KαX-ray intensity ratio values. We also show that Zn–Fe alloy mi nimum microstrain value corresponds to the maximum changes in KβX-ray production cross-section values of Fe and Zn. Copyright © 2017 John Wiley & Sons, Ltd.

Effects of pH Value of the Electrolyte and Glycine Additive on Formation and Properties of Electrodeposited Zn-Fe Coatings

Environmentally friendly and cyanide-free sulfate bath under continuous current and the corrosion behavior of electrodeposits of zinc-iron alloys were studied by means of electrochemical tests in a solution of 3.5% NaCl in presence and absence of glycine. The effects of pH on the quality of Zn-Fe coatings were investigated in order to improve uniformity and corrosion protection performance of the coating films. The deposit morphology was analyzed using scanning electron microscopy (SEM), and X-ray diffraction (XRD) was used to determine the preferred crystallographic orientations of the deposits. It was found that the uniformity and corrosion resistance of Zn-Fe coating films were strongly associated with pH of the coating electrolyte. To obtain the effect of pH on the film quality and corrosion performances of the films, the corrosion test was performed with potentiodynamic anodic polarization method. It was also observed that uniformity and corrosion resistivity of the coating films were decreased towards pH = 5 and then improved with increasing pH value of the electrolyte. The presence of glycine in the plating bath decreases the corrosion resistance of Zn-Fe coatings.

Zn-Fe alloy electrodeposition from chloride bath: Influence of deposition parameters on coatings morphology and structure

In this study, the kinetics of Zn–Fe codeposition was investigated in chloride acidic solution using cyclic voltammetry. Anomalous codeposition is detected and this mechanism depends on the Zn(II)/Fe(II) concentration ratio in the electrolytic bath. Influence of deposition parameters on the morphology and structure of the coatings is discussed using characterization techniques and using the anodic linear sweep voltametry (ALSV). The ratio between Zn(II)/Fe(II) considerably influences the structure of the alloys. Dense, uniform, and single-phased Zn–Fe coatings could be obtained.

Optimization of deposition conditions for bright Zn-Fe coatings and its characterization

Sulfate bath having ZnSO4 · 7H2O, Fe2(SO4)3 · H2O and thiamine hydrochloride (THC) and citric acid (CA) in combination, represented as (THC + CA) was optimized for deposition of bright Zn-Fe alloy coating on mild steel. Bath constituents and operating parameters were optimized by standard Hull cell method, for peak performance of the coating against corrosion. The effect of current density (c.d.), pH and temperature on deposit characters, such as corrosion resistance, hardness and glossiness were studied and discussed. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods were used to assess the corrosion behaviors. Surface morphology, and composition of the coatings were examined using Scanning Electron Microscopy (SEM), interfaced with EDXA facility, respectively. The Zn-Fe alloy, with intense peaks corresponding to Zn(100) and Zn(101) phases, showed highest corrosion resistance, evidenced by X-ray diffraction (XRD) study. A new and cheap sulfate bath, for bright Zn-Fe alloy coating on mild steel has been proposed, and results are discussed.

High Anticorrosion Nano Zn-Fe Coatings by Pulse Electrodepositing

Nano Zn-Fe coatings in a chloride electrolyte with additives by reverse pulse current were obtained and the anticorrosion was investigated. The morghology and crystal size of Zn-Fe alloy depositions were measured by scanning electron microscope and atom force microscope. Coatings with 30 nm or so crystal size was obtained with mean current density 9.0 A•dm-2, duty cycle 60%, frequency 500 Hz and time of negative to positive 30 ms ∶8 ms. It was detected by X-ray diffraction that the pulse plated coatings of Zn–Fe were mixtures of two phases, one of them being the α-phase and the other pure zinc or the α-phase with a significantly lower proportion of Fe. The pulse plated Zn-Fe coatings’ corrosion resistance was greatly improved compared with Zn-Fe coatings by direct current according to Tafel tests, saline immersion and salt spray tests. The anticorrosion of Zn-Fe coatings with 30 nm crystal size was 2~3 times than that of normal Zn-Fe alloy deposits.

Composition Modulated Multilayer Zn–Fe Alloy Coatings on Mild Steel for Better Corrosion Resistance

Composition modulated alloy (CMA) of Zn–Fe coatings were developed on mild steel galvanostatically from chloride bath containing sulphanilic acid (SA) and ascorbic acid (AA) through single bath technique (SBT). The properties of CMA coatings were found to depend on the thickness of individual layers and switching cathode current densities (SCCDs). The CMA (Zn–Fe) coating, having 120 layers, deposited at 20 and 50 mA cm−2, were found to show the least corrosion rate (1.545 × 10−2 mmy−1) compared to monolithic alloy (32.5 × 10−2 mmy−1) of the same thickness. The improved corrosion resistance of multilayered coatings was due to the fact that the defects and failures occurring in a single layer in the deposition process is covered by the successively deposited coating layers, and hence the corrosive agent path is extended or blocked. Further, the high corrosion resistance of CMA Zn–Fe coatings was attributed to the “dielectric barrier” of the coatings, evidenced by dielectric spectroscopy and Mott–Schottky's plot. The corrosion rate was found to increase at high degree of layering, and is attributed to less relaxation time for redistribution of metal ions in diffusion layer, during plating. In other words, at higher layer thickness, the CMA coating tends to become a monolithic. CMA coatings were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM).

Electrodeposition of Zn–Ni, Zn–Fe and Zn–Ni–Fe alloys

Zn–Fe, Zn–Ni and Zn–Ni–Fe coatings were electrodeposited galvanostatically on mild steel from acidic baths (pH 3.5) consisted of ZnCl2, NiCl2, FeCl2, gelatin, sulfanilic (p-aminobenzenesulfonic) acid and ascorbic acid. Cyclic voltammetry showed that the effect of gelatin was more pronounced than that of sulfanilic acid, and that the deposition of the ternary alloy behaved differently from the deposition of the binary alloys. In all three systems, the Faradaic efficiency was higher than 88%, the rate of Zn deposition was heavily influenced by mass-transport limitation at high applied current densities, and the deposition was of anomalous type. For each applied current density, the concentrations of Ni and Fe in the ternary alloy were higher than the corresponding concentrations in the binary alloys. The hardness of Zn–Ni coatings was the highest, while that of Zn–Fe coatings was the lowest. The Zn–Ni–Fe coatings were the smoothest, had distinguished surface morphology, and contained ZnO in the bulk, not just on the surface. The lowest corrosion rate in each alloy system (214, 325 and 26μm year−1 for Zn–Ni, Zn–Fe and Zn–Ni–Fe, respectively) was characteristic of coatings deposited at 30, 30 and 40mAcm−2, respectively. The higher corrosion resistance of the ternary alloy was also reflected by a higher corrosion potential, a higher impedance and a higher slope of the Mott-Schottky line. The enhanced corrosion behavior of the ternary alloy was thus attributed to its chemical composition, phase content, roughness and the synergistic effect of Ni and Fe on the n-type semiconductor surface film.

Pulse plating effect on composition and corrosion properties of zinc alloy coatings

The influence of pulse plating parameters on the chemical and phase composition, surface topography and corrosion resistance of Zn–Ni (∼12%Ni), Zn–Co (<1%Co) and Zn–Fe (<1%Fe) alloy coatings has been studied. Pulse plating of Zn alloys resulted in different outcomes for Zn–Ni and low alloyed (Zn–Co and Zn–Fe) coatings. Non-stationary crystallisation resulted in formation of single phase γ-Zn21Ni5 coatings, while two different phases of Zn were produced during Zn–Co and Zn–Fe deposition. Pulse plated Zn–Ni coatings possessed from two to three times smaller grain size and at the same time, corrosion currents half those of the direct current deposits. However, the reduction in the grain size of Zn–Co and Zn–Fe coatings was not accompanied by any reduction in the corrosion current of these alloys. It is suggested that the dual phase formation was the principal reason why pulse plated low alloyed Zn coatings did not exhibit improvement in their corrosion resistance.

Electrodeposition of decorative and protective Zn–Fe coating onto low-carbon steel substrate

Cyclic voltammetry and chronoamperometry were performed in conjunction with SEM technique to study the electroplating process of Zn–Fe alloys. The technological parameters for Zn–Fe electroplating have been optimized and the smooth Zn–Fe coatings with high corrosion resistances were obtained. The results also show that, under our experimental conditions, the deposition of Zn–Fe behaved anomalously and followed the mechanism of three-dimensional (3D) nucleation. With the increase of deposition potential, the grain growth changed from progressive to instantaneous. Meanwhile, a new viewpoint was proposed to explain the anomalous co-deposition behavior of Zn–Fe coatings.

Corrosion behaviour of chromated Zn and Zn alloy electrodeposits

The influence of a chromate film on the corrosion behaviour of Zn, Zn–Co and ZnFe coatings was investigated. XPS, AES techniques were applied for characterisation of the iridescent chromate films, while the XRD method was used for the corrosion product analysis. Atmospheric field (4 years data), accelerated (neutral salt spray and SO 2 cabinet) tests and electrochemical measurements were applied for the corrosion resistance studies. The beneficial influence of alloying for chromated Zn electrodeposits was observed under the conditions, where Cl − ions were the dominant pollutant (marine test site, Cl − cabinet, Cl − aqueous solution). The degree of protection from the chromate film, in spite of their lower thickness, was detected to be higher for the alloyed samples. A higher concentration of Cr(VI) compounds in the passive chromate layers of alloyed samples may be the reason of their superior corrosion resistance.

Corrosion Behaviour of Zn and Zn Alloy Coatings in Alkaline Media

SUMMARYThe corrosion behaviour of electrodeposited Zn, Zn-Co, Zn-Fe and Zn-Ni coatings without and with Chromate films was studied in alkaline solutions and mortar probes. DC polarization measurements were used for electrochemical characterization of the investigated samples, while AES XPS techniques were applied for the Chromate film analysis. The stability of the anodically formed oxide films on unchromated coatings appeared to be dependent on their composition. The oxide layer stability in Cl free NaOH solution was higher for Zn-Ni and Zn-Co alloys, while introduction of Cl ions caused lowering of stability especially for Zn-Ni coating. The detected corrosion current values implied that unchromated Zn alloys did not possess higher corrosion resistance in alkaline media containing Cl ions. Meanwhile, chromated Zn-Co coatings exhibited the beneficial effect of alloying for corrosion in alkaline solutions and concrete. A higher concentration of Cr(Vl) compounds in the passive Chromate layer of the alloyed sample may be the reason for its superior corrosion resistance.