Zn-Fe Alloy Research Articles

Electrodeposition Behavior of Zn–Fe Alloy from Zincate Solution Containing Triethanolamine

Electrodeposition behavior of ZnFe alloys was investigated at current densities of 10500 A・m-2 and a charge of 5×104 C・m-2 in an unagitated zincate solution containing triethanolamine, which forms a stable complex with Fe2+ ions at 308 K. The content of Fe in deposit changed significantly depending on the current density. At lower current densities than 20 A・m-2, the content of Fe was approximately 90 mass, that is, the ZnFe alloy exhibited normal codeposition, wherein electrochemically more noble Fe deposited preferentially, while at higher current densities than 100 A・m-2, it exhibited anomalous codeposition, wherein less noble Zn deposited preferentially. The current density, at which the content of Fe in deposit changed significantly, corresponded to the one, at which the cathode potential in total polarization curve abruptly shifted to the less noble region than the equilibrium potential for Zn deposition. Iron deposition and H2 evolution were significantly suppressed in the region of anomalous codeposition at higher current densities, showing the formation of an inhibitor for deposition, which results from Zn2+ ions in the cathode layer. The current efficiency for alloy deposition was not close to zero even in the region of normal codeposition, and the content of Fe in the region of anomalous codeposition was close to the composition reference line, which shows the different deposition behavior from the sulfate solutions. In the region of normal codeposition at lower current densities, the underpotential deposition of Zn occurred with Fe. TEM analysis revealed that ZnFe alloys deposited at lower current densities were composed of a stable intermetallic compound of Fe5Zn21. The activity coefficient of Zn in the deposit appears to decrease remarkably because of the formation of a stable Fe5Zn21. [doi:10.2320/jinstmet.J2014054]

トリエタノールアミンを含むジンケート浴からの Zn-Fe 合金電析挙動

Electrodeposition behavior of Zn-Fe alloys was investigated at current densities of 10-500 A•m−2 and a charge of 5×104 C•m−2 in an unagitated zincate solution containing triethanolamine, which forms a stable complex with Fe2+ ions at 308 K. The content of Fe in deposit changed significantly depending on the current density. At lower current densities than 20 A•m−2, the content of Fe was approximately 90 mass%, that is, the Zn-Fe alloy exhibited normal codeposition, wherein electrochemically more noble Fe deposited preferentially, while at higher current densities than 100 A•m−2, it exhibited anomalous codeposition, wherein less noble Zn deposited preferentially. The current density, at which the content of Fe in deposit changed significantly, corresponded to the one, at which the cathode potential in total polarization curve abruptly shifted to the less noble region than the equilibrium potential for Zn deposition. Iron deposition and H2 evolution were significantly suppressed in the region of anomalous codeposition at higher current densities, showing the formation of an inhibitor for deposition, which results from Zn2+ ions in the cathode layer. The current efficiency for alloy deposition was not close to zero even in the region of normal codeposition, and the content of Fe in the region of anomalous codeposition was close to the composition reference line, which shows the different deposition behavior from the sulfate solutions. In the region of normal codeposition at lower current densities, the underpotential deposition of Zn occurred with Fe. TEM analysis revealed that Zn-Fe alloys deposited at lower current densities were composed of a stable intermetallic compound of Fe5Zn21. The activity coefficient of Zn in the deposit appears to decrease remarkably because of the formation of a stable Fe5Zn21.

Effect of bismuth and strontium interaction on the microstructure development, mechanical properties and fractography of a secondary Al–Si–Cu–Fe–Zn alloy

Abstract The effect of various additions of bismuth and strontium on the microstructure characteristics, impact and tensile properties, as well as fracture behaviour of a secondary Al–Si–Cu–Fe–Zn under as-cast condition are systematically investigated in this study. The as-cast samples were examined using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Microstructural analyses showed the occurrence of interaction between Bi and Sr, which, significantly, led to the change of eutectic Si morphology from fibrous to flake morphology, with an increase of mean length, area, and shape factor, an alteration of crystallographic orientation, and an increase in twin density. The mechanical properties were investigated by hardness, impact, and tensile tests with various concentrations of Bi and Sr. It was found that the highest mechanical properties obtained for Sr/Bi were for a ratio of more than 0.44, while deterioration occurred at a ratio of less than 0.32. The hardness, impact toughness, ultimate tensile strength (UTS), elongation to fracture (El), and quality index (Q) of alloys decreased by 7%, 62%, 19%, 57% and 48% respectively when the Sr/Bi ratio diminished from 0.44 to 0.32. The fracture behaviour of impact samples with an Sr/Bi ratio of more than 0.44 showed clear ductile fracture, while the specimens with an Sr/Bi ratio of less than 0.32 presented brittle fracture that corresponds to impact toughness values. Furthermore, the fracture surfaces of tensile samples revealed that the dimple ductile fracture transformed to cleavage brittle mode with drop of the Sr/Bi ratio to less than 0.32 due to an increase in the length, area, and shape factor of eutectic Si. Additionally, the interaction mechanism between Bi and Sr are also discussed in this study.

Use of n-type semiconductor silicon as substrate material for electrodeposition of Zn1−xFex alloy thin films

Zn1−xFex alloys were electrochemically deposited on semiconductor silicon substrates from sulfate bath. Effect of bath composition on phase formation, chemical composition, crystallite shape, electrical resistivity and magnetoresistance were investigated using appropriate characterization tools. It was shown that Zn–Fe alloys can be successfully deposited directly on semiconductor silicon substrate using electrodeposition technique. Iron content in films influences crystallite size, resistivity and magnetoresistance of films.

Enhancement of strength and ductility of Cu–Sn–Zn alloy by iron addition

Effects of iron addition to Cu–Sn–Zn alloy on the microstructures and mechanical properties were investigated. The Cu–Sn–Zn–Fe alloy, aged at 500°C for 4h, showed a peak hardness and an excellent combination of strength and ductility; e.g. a yield strength of 264MPa, an ultimate tensile strength of 514MPa and a fracture elongation of around 50%. The precipitates responsible for the strengthening are identified as bcc Fe with diameters ranging from 20 to 60nm, and the interfacial relationship between the precipitate and copper matrix is (002)M//(110)P. It is discussed that Orowan dislocation bypassing can be a dominant strengthening mechanism; quantitative calculations for strengthening due to precipitation and grain refinement are roughly similar to the experimental results of the present Cu alloy. Additionally, the high work-hardening rate in a peak aged condition can be responsible for high tensile ductility of the alloy.

Fe-Zn Alloy Coating on Galvannealed (GA) Steel Sheet to Improve Product Qualities

Galvannealed steel sheets (GA) have become the mainstream steel sheet for automobile applications because of their superior corrosion resistance, paintability, and weldability. To impart specific properties, different coatings on GA steel sheet were reported to improve properties further. In this context, we have developed an electroplating process (flash coating) for bright and adherent Fe-Zn alloy coating on GA steel sheet to enhance performances such as weldability, frictional behavior, phosphatability, and defect coverage. A comparative study with bare GA steel sheet was carried out for better elastration. The electroplating time was reduced below 10 s for practical applicability in an industrial coating line by modulating the bath composition. Electroplating was performed at current density of 200-500 A/m2 which yielded with higher cathode current efficiency of 85-95%. The performance results show that Fe-10 wt.% Zn-coated GA steel sheet (coating time 7 s) has better spot weldability, lower dynamic coefficient of friction (0.06-0.07 in lubrication), and better corrosion resistance compared to bare GA steel sheet. Uniform phosphate coating with globular crystal size of 2-5 µm was obtained on Fe-Zn flash-coated GA steel sheet. Hopeite was the main phosphate compound (77.9 wt.%) identified along with spencerite (13.6 wt.%) and phosphophyllite (8.5 wt.%).

Adhesion Mechanism of Galvannealed Steel Sheet during Flat Sliding Test Studied by Microscopic Analysis of Die Surfaces

The surfaces of dies used for flat sliding tests of galvannealed steel sheet (GA) have been investigated using several electron microscopic techniques in order to clarify the adhesion mechanism. Two kinds of adhesive materials were identified on the die surface. One consists of an Al oxide – Fe–Zn alloy composite and tightly bonds to ridges of the die surface. This resembles the built-up edges formed on tool surfaces during metal-cutting operations. Another adhesive material is composed of Fe–Zn alloys located in the hollows of the die surface which do not bond or only loosely bond to the die surface. A new adhesion model consisting three steps is proposed; (1) the Al oxide – Fe–Zn alloy composite layers are formed on the ridges of the die surface. (2) The Fe–Zn intermetallics on the GA surfaces are cut by this layer and (3) accumulate in the hollow of the die surface.

Avaliação da resistência à corrosão de eletrodepósitos de liga ZnFe sobre aço tratado com filmes contendo sais de terras raras e silanos BTSE, BTESPTS

O presente trabalho tem como objetivo avaliar a resistência a corrosão do aço revestido com eletrodepósito de liga ZnFe tratado com filmes constituídos de uma pré-camada obtida através de solução de sais de terras raras (Ce ou La) acrescida de filmes de silanos bis 1,2-[trietoxissilil]etano) (BTSE) e/ou bis-(3-[trietoxissilil]-propil) - tetrassulfeto (BTESPTS). Esses sistemas foram avaliados através das Curvas de Polarização, Espectroscopia de Impedância Eletroquímica (EIE), Microscopia Eletrônica de Varredura (MEV) e Espectrometria de Energia Dispersiva (EDS). Os resultados de EIE e polarização indicaram que os sistemas estudados foram eficientes contra corrosão e que seu desempenho depende do tipo de cátion do sal. O sistema ZnFe+Ce+BTSE+BTESPTS mostrou o melhor resultado contra corrosão.

The Effect of Selective Oxidation On Galvanizing and Galvannealing Reactions of Dual-Phase Steels

Dual Phase Steels (DP steels), which have high strength with an excellent formability, offer potential for weight savings in the automotive industry because of their high strength and excellent formability. Alloying elements, such as Mn, Mo, Si, and Cr, are commonly added in DP steels. The alloy elements not only enhance the mechanical properties of the steel substrate, but also play an important role in the following GI and GA process. In this work, two kinds of DP steels were used, labeled HDA and HDB, in which HDB had more Mn, Si, Cr than HDA. Further GA treatments resulted in more Fe-Zn IMCs for HDA than HDB samples. This retardation in the Fe-Zn alloy reaction in HDB can be attributed to the selective oxidation at the steel surface during the annealing process prior to hot dipping. Those external selective oxides were too small to be observed by the SEM, but can be confirmed by TEM observations and OCP tests. Moreover, GDOES analyses clearly revealed that those IMCs were formed by the transformation from the Fe-Al inhibition layer.

Influence of additive on nanocrystalline, bright Zn–Fe alloy electrodeposition and its properties

The nanocrystalline, bright Zn–Fe alloy electrodeposit was prepared by using additive, condensation product of veratraldehyde and valine (VV). Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis in the presence of an additive showed nanocrystalline nature of deposit. These studies also revealed the change in surface morphology, phase composition and orientation of coating. The additive, increases faradaic efficiency and throwing power of plating bath. In addition, appearance, hardness, adherence, ductility and corrosion resistance of Zn–Fe alloy deposit are also improved in the presence of the additive. Simultaneously, at different current densities both faradaic efficiency and throwing power increase to peak values, 91% and 23%, respectively, and thereafter decrease. The iron content and hardness of the bright coating change with applied current density. The lower corrosion resistance of bright Zn–Fe deposit at higher current density was reflected by more negative corrosion potential and lower impedance.

A novel iron enrichment isothermal kinetic model proposal for galvanneal coatings

Galvanneal (GA) coatings are extensively used in the automotive industry in car bodies and for exposed parts to enhance corrosion protection. GA coatings are produced in Continuous Galvanizing Lines (CGL) by carrying out a heat treatment immediately after the Zn deposition in the liquid state, where the liquid is constitutionally solidified and transformed into Fe–Zn alloy (composed by its intermetallic compounds (IMCs)). IMCs nucleation and growth kinetics control allows one optimize the coating mechanical performance during steel drawing operations. This work proposes a new kinetic model to describe the GA coating Fe enrichment. Based on the hypothesis that each IMC will be nucleated, Fe enriched, saturated and consumed by an Fe richer IMC, the model was able to describe the Gleeble simulated isothermal Fe enrichment kinetics for unalloyed industrially produced interstitial free (IF) and dual-phase (DP) GA coating steels.

A comparison of genetic programming and neural networks; new formulations for electrical resistivity of Zn–Fe alloys

It is difficult to automatically solve a problem in a systematic method without using computers. In this study, a comparison between Neural Network (NN) and genetic programming (GEP) soft computing techniques as alternative tools for the formulation of electrical resistivity of zinc–iron (Zn–Fe) alloys for various compositions is proposed. Different formulations are supplied to control the verity and robustness of NN and GEP for the formulation to design composition and electrolyte conditions in certain ranges. The input parameters of the NN and GEP models are weight percentages of zinc and iron in the film and in the electrolyte, measurement temperature, and corrosion voltage of the films. The NN- and GEP-based formulation results are compared with experimental results and found to be quite reliable with a very high correlation (R 2=0.998 for GEP and 0.999 for NN).

A Study of Double-Coating of Hot-Dip Aluminizing

Double-coating of hot-dip aluminizing is a process of protecting steel from being oxidized. The process is featured that the component is firstly hot-dip galvanized and finally hot-dipped with aluminum. The comparison of interface morphology was conducted for single hot-dip aluminizing and double-coating of hot-dip aluminizing on Q235 steel sheets. The metallographies of the cross-sections were observed and analyzed with SEM, XRD and EDS, respectively for the specimens prepared by the two processes. The experimental results indicate that there is no Zn-Fe alloy layer formed in the double-coating, and both single and double coating have similar phase compositions. However, the interface between the alloy layer and the steel matrix is smoother for the double-coating than that for single-coating.

Estudo do desempenho de filmes contendo sais de terras raras como inibidores de corrosão da liga ZnFe eletrodepositada sobre aço

Aço revestido com eletrodepósitos de liga ZnFe é um material de uso comum na indústria de construção civil e automotiva. O revestimento à base de zinco necessita, entretanto, ser protegido de ambientes corrosivos através de um tratamento de superfície que geralmente contém cromo hexavalente (Cr6+), tóxico para o meio ambiente e cancerígeno para o homem. O presente trabalho apresenta um estudo com inibidores de corrosão contendo terras raras (Ce ou La), sobre aço revestido com eletrodepósitos de liga ZnFe. Esses filmes foram avaliados através das Curvas de Polarização, da Espectroscopia de Impedância Eletroquímica (EIE), da Microscopia Eletrônica de Varredura (MEV) e Espectrometria de Energia Dispersiva (EDS). A espectroscopia fotoelétrica de emissão de raios-X (XPS) também foi utilizada para comprovar a presença desses filmes contendo óxidos sobre a superfície da liga ZnFe. Os resultados de EIE e polarização indicaram que as camadas estudadas foram eficientes contra corrosão e que seu desempenho dependia do tipo de cátion presente no sal. A amostra representada por Ce+ZnFe mostrou o melhor desempenho na proteção contra a corrosão, havendo um decréscimo de aproximadamente 10 vezes na densidade de corrente quando a liga foi medida com Ce+ ZnFe um aumento de IZI em uma ordem de grandeza.

Toward Sustainable Progress of Galvanized Steel Sheets

Steel, used in from familiar products such as automobiles and electrical appliances to large structures such as buildings and ships, is inextricable and basic materials of our lives. Steel has made significant progress in both quantity and quality with the development of society. Galvanized steel has evolved most significantly in these 20 or 30 years, being recognized that the steel is the most suitable material for automobiles, with rapid increase in automotive production and emerging demand of anti-corrosion bodies for a background.In this paper, the author firstly would like to describe the development details of galvanized steel, particularly GA (Galvannealed Steel: Hot-dip Zn-Fe alloy steel) achieved through cooperative work among automotive companies, steel companies and paint companies in Japan. At present, galvanized steel became one of the biggest shipping steel products in Japan and in the world as well.If the strong demand for galvanized steel continues in the future like today, it is said that the zinc source will be depleted in 20 years. Aluminum is thought to be the most probable alternative element for zinc, but there are still several problems in its substitution. Eventually, as a tentative measure, only remedy for this matter is to save zinc resources and therefore the development of both hot-dip and electro galvanizing process which makes possible to reduce the zinc usage is required.

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).

New Brightener for Zn-Fe Alloy Plating from Sulphate Bath

Zn-Fe alloy electrodeposition was carried out in the presence of condensation product 2-{[(1E)-(3,4-dimethoxyphenyl)methylidene]amino}-3-hydroxypropanoic acid formed between veratraldehyde and serine in acid sulphate bath. Hull cell was used for optimizing the operating parameters and bath constituents. During deposition, the potential was shifted towards cathodic direction in the presence of addition agents and brightener. The polarization studies show that deposition taking place in basic bath and optimum bath was 1.08 and 1.15 V, respectively. Current efficiency and throwing power were reached around 85% and 26%, respectively. The SEM images of bright deposit indicated its fine-grained nature and appreciable reduction in the grain size. XRD studies have showed that the grain size of the deposit generated from optimum bath was 16 nm. UV-visible spectroscopic studies confirm the formation of complex between metal ion and brightener.

Analysis and Calculation of Electrodeposition Process of Zn Alloy Coatings

Electrodeposited Zn-Fe alloy coating has good anti-corrosion performance and has been widely applied to protect steel materials from corrosion. In this paper, Zn-Fe alloy coatings were plated from acidic sulphate bath, and the relationship between real concentration of metallic complexes ([ZnL+] and [FeL+]) in the bath, which was calculated through solving nonlinear equations by METLAB software, and components of alloy coatings was studied. When ZnSO4•7H2O added in the bath increases from 10 g/L to 50 g/L, the ratio of ferrous complex to total complex decreases from 81.96% to 46.76%, simultaneously the iron content in Zn-Fe alloy coatings decreases from 26.82% to 6.32%. As FeSO4•7H2O and (NH4)2SO4 added in the bath increases from 40 g/L to 80 g/L respectively, the ratio of ferrous complex to total complex increases from 50.02% to 66.23% and from 58.65% to 60.37% respectively, simultaneously the iron content in coatings increases from 8.26% to 13.77% and from 9.28% to 11.92% respectively. The results show that variation of concentration of metallic complexes in the bath can lead to variation of components of coating proportionally.