Zn Al Coatings Research Articles

Aspects on Early-Stage Corrosion of Different Zinc Alloys: Wet scCO2-Induced Corrosion

The surface activity of different zinc alloys was evaluated in wet scCO2. The zinc coating surface chemistry governed the corrosion product formation. On zinc and Zn-Al coatings, the Al2O3 layer prevented growth of corrosion products. A Zn-Al-Mg coating showed high initial reactivity due to active Zn-Mg phases. An electrogalvanized coating was very active due to a high ratio of exposed, less dense planes. In a Zn-Fe coating, several Zn-Fe phases were susceptible to wet scCO2 at the same time, triggering the sacrificial effect of Zn. Wet scCO2 is a convenient medium to assess the early-stage corrosion of metal coatings.

Flame-sprayed Zn-Al coatings on ABS without chemical surface preparation

Metallization of polymeric materials is a process that manages to combine the properties of polymers and metals, to expand its range of applications. In this research, the deposition of a Zn-Al alloy on a polymeric substrate (ABS) using wire flame spray was carried out, with a predominant advantage by not using chemical surface preparation processes, thus obtaining materials at low cost, friendly to the environment, without affecting the properties of the substrate, avoiding its degradation by temperature, and gaining a level of electrical conductivity appropriate to nature of the coatings. Substrate roughness is measured by interferometry, coating morphology by SEM, the composition by EDS, structure by XRD, adhesion by Pull-Off, and electrical resistivity is evaluated using the 4-point test. The SEM results show a coating with a thickness of the order of 89 µm, homogeneous in its composition with a Zn and Al crystalline structure, an adhesion strength of 888 N, with a porosity of 0.87% with an average pore size of 10 µm. The electrical conductivity study of the coated material shows a good electrical response, with a value of 2682 S/m.

Properties of Zn-Al-Mg-TiO2 coating prepared by cold spraying

Improving the property of coating is the focus of current marine protection research. In this paper, the Zn-Al-Mg-TiO2 and ZnAl coatings were prepared by cold spraying. The wear, electrochemical experiment and methyl blue degradation tests were carried out to study the tribological, anticorrosive and antifouling properties of coatings. The microstructure, composition, and wear scar of coatings were analyzed by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and white-light interferometer. The results showed that the wear mechanism of the Zn-Al-Mg-TiO2 coating was mainly abrasive wear, and the wear property of the Zn-Al-Mg-TiO2 coating was better than ZnAl coating. Compared with the ZnAl coating, Zn-Al-Mg-TiO2 coating had lower corrosion current density. In addition, the Zn-Al-Mg-TiO2 coating can rapidly degrade methyl blue in a UV-rich environment, but ZnAl coating did not.

Effect of machine hammer peening on the surface integrity of a ZnAl-based corrosion protective coating

Thermally sprayed protective coatings are applied onto many mechanically stressed components such as support structures, shafts, turbine blades or heat exchangers. In addition to the static or cyclic load, a superimposition with corrosion processes occurs in many cases. Thermal sprayed ZnAl coatings are known for their performant corrosion protection properties. Within this context, the potential of ZnAl-based layer systems was analyzed regarding corrosion fatigue behavior. Therefore, a timeand cost-efficient testing strategy based on a corrosion-superimposed load increase procedure was used to estimate the effects of a corrosive attack during cyclic loading. The investigated coating systems were thermally sprayed and partially post-processed with a Machine Hammer Peening (MHP) operation. This treatment was identified as an appropriate technique for compressing and smoothing coated surfaces. The inter-relationships between the parametrization of the MHP process, the resulting surface integrity, and the estimated corrosion fatigue properties were analyzed. The investigations indicate a positive effect of MHP post-processing operations on the surface properties of the ZnAl-based coating system.

Investigation on Relationship Between Microstructural Characteristics and Mechanical Properties of Wire-Arc-Sprayed Zn-Al Coating

Wire arc spraying is a cost-effective thermal spraying technology to deposit a protective coating layer on the surface of industrial components. Mechanical properties of wire arc spraying coatings are mainly influenced by their heterogeneous microstructure, resulting in complex and anisotropic mechanical properties. The objective of this investigation is to characterize the mechanical behavior of wire-arc-sprayed Zn-15Al alloy using an efficient micromechanical–computational scheme. Scanning electron microscopy images were imported to an object-oriented finite element scheme and distinguished into various phases, and then subsequently discretized into finite elements. To examine the validity of this technique, experimental studies, such as Knoop and Vickers microhardness, resonance frequency, and nanoindentation, were conducted on the freestanding coating samples. The elastic modulus of the coating was also calculated using well-known analytical methods. Comparison of the results obtained in this study was used to investigate the relationship between the microstructural features and mechanical properties in coating materials. Image-based finite element analysis showed good agreement with the experimental measurements and proved the effect of splat boundaries on the reduction in mechanical strength between coating layers and, consequently, lower elastic modulus of the wire-arc-sprayed Zn-15Al coating in the longitudinal direction compared to the transversal one.

Synthesis, microstructural, corrosion and antimicrobial properties of Zn and Zn–Al coatings

ABSTRACTDevelopment of a new coating named ‘Zincal’ is introduced for future smart cities’ infrastructures. Pure Zn and newly developed ‘Zincal’ (a composition of Zn–Al) thermal sprayed (TS) coatings were applied onto low-carbon steel to investigate coating’s life against the corrosive and dusty environment for future smart cities’ infrastructures (big bridges, buildings, poles, stadiums, railway structures etc.). Therefore, for both coatings, salt spray humidity and microbial tests were carried out. The result shows that Zincal coating has promising anti-corrosion properties under combat microbiological corrosion attack and is also suitable in the humid and salt containing environment.

Preparation and corrosion resistance of chromium-free Zn-Al coatings with two different silane coupling agents

In this paper, the chromium-free Zn-Al coatings prepared with different mixing ratios of 3-glycidoxypropyltrimethoxy (GPTMS) and methyltrimethoxysilane (MTMS) were presented. The morphology, composition and formation mechanism of the coatings were observed and studied by using scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR) and thermal analysis. Polarization tests and immersion tests were used to study the corrosion resistance of the coatings. The results showed that the coatings had similar morphology to Dacromet coatings. The silane molecules were hydrolyzed and condensed to form three-dimensional cross-linking networks. The coatings with GPTMS had nobler corrosion potential and lower corrosion current density. The immersion time of the coating in the 5 wt% NaCl solution could reach 58 days when the mixing ratio of GPTMS/MTMS was equal to 1.

Atmospheric corrosion of Zn–Al coatings in a simulated automotive environment

ABSTRACTAccelerated NVDA (VDA 233-102) tests were performed on bare Zn and Al sheets, Galfan coating (Zn–5 wt-% Al) and Galvalume coating (Zn–55 wt-% Al) on steel. ZnO, Zn(OH)2 and Zn5(OH)8Cl2·H2O were the main corrosion products identified on both bare Zn sheet and Galfan. AlOOH and Al(OH)3 were preferentially formed on bare Al sheet and Galvalume. In addition, Zn–Al–containing corrosion products, Zn6Al2(OH)16CO3·4H2O and/or Zn2Al(OH)6Cl·2H2O were identified on both Galfan and Galvalume. Corrosion products of Zn6Al2(OH)16CO3·4H2O with a platelet morphology were preferentially formed in the zinc-rich interdendritic regions of the Galvalume surface. Galfan revealed a similar corrosion behaviour as bare Zn sheet, whereas Galvalume exhibited similar behaviour as bare Al sheet. Deposition of chlorides highly influenced the corrosion of both Galvalume and Al rather than Galfan and Zn due to the rapid local damage of the compact native thin film of Al2O3.

Structure and Corrosion Behavior of Arc-Sprayed Zn-Al Coatings on Ductile Iron Substrate

In this research, four coatings including pure zinc, pure aluminum, a double-layered coating of zinc and aluminum, and a coating produced by simultaneous deposition of zinc and aluminum were deposited on a cast iron substrate using electric arc-spraying technique. The coatings were characterized by XRD, SEM and EDS map and spot analyses. Adhesion strength of the coatings was evaluated by three-point bending tests, where double-layered coating indicated the lowest bending angle among the specimens, with detection of cracks at the coating–substrate interface. Coatings produced by simultaneous deposition of zinc and aluminum possessed a relatively uniform distribution of both metals. In order to evaluate the corrosion behavior of the coatings, cyclic polarization and salt spray tests were conducted. Accordingly, pure aluminum coating showed susceptibility to pitting corrosion and other coatings underwent uniform corrosion. For double-layered coating, SEM micrographs revealed zinc corrosion products as flaky particles in the pores formed by pitting on the surface, an indication of penetration of corrosion products from the lower layer (zinc) to the top layer (aluminum). All coatings experienced higher negative corrosion potentials than the iron substrate, indicative of their sacrificial behavior.

Atmospheric Corrosion of Zinc-Aluminum Alloyed Coated Steel in Depleted Carbon Dioxide Environments

NaCl induced corrosion of Zn-0.2Al, Zn-5Al and Zn-55Al coated steel was investigated at low and ambient CO2 levels. Weight loss measurements revealed an enhancement of the corrosion of Zn-0.2Al and particularly Zn-5Al in low CO2. This was connected to an increase of surface pH in a low CO2 atmosphere promoting the formation of ZnO and layered double hydroxide for Zn-5Al. For Zn-55Al, CO2 depletion did not affect the surface pH due to the acidification effect of Al3+. Preferential dissolution of zinc rich phase was observed on cross-sections, particularly in depleted CO2 experiments. Different sequences of corrosion product formation were proposed for the different Zn-Al coatings.

Designing the corrosion products of ZnAl15: a new approach to smart corrosion protection coatings?

ZnAl coatings are known to provide reliable corrosion protection for low-grade structural steels in most environments. Depending on the coating process, different phase compositions can be observed in such coatings. In case of thermal spraying, the high cooling rates were proven to result in the formation of metastable β-ZnAl for the first time in literature. To assess the influence on the corrosion behaviour, β-ZnAl and α-η-ZnAl samples were produced and corroded in a salt spray test. A pronounced influence of the phase composition on the formation of layered double hydroxides was observed.

The effect of silicon on spangle size in hot-dipped 55 wt%Al-Zn coatings

The effect of various silicon levels on spangle size in hot-dipped 55wt%Al-Zn-xSi (x=0.5, 1.0, 1.6, 2.0, 4.0, all in wt%) coatings was studied. The results showed that as silicon content was increased from 0.5 to 4.0wt%, spangle size increased gradually from the minimized range to the normal range. Spangle range transition occurred in silicon content between 1.0 and 1.6wt%. Correlation between intermetallic species and spangle sizes under various silicon contents was investigated. It was found that in the process of spangle size from the minimized to the normal, intermetallic species of the alloy layer were also subject to a regular change of phase transformation from FeAl3 to τ5 (also refers to α-AlFeSi), especially remarkable in the range of silicon content where spangle range transited. Phase evolution of the intermetallic layer in various silicon levels was quantitatively analyzed by thermodynamic modelling using Pandat software package, which provided a deep understanding of how the silicon content affect the formation of intermetallic species and controlled the change of intermetallic layer underneath the overlay. First-principles calculations were performed to evaluate the lattice mismatch between intermetallic species and primary α-Al, which gave an interpretation of how the intermetallic species influenced the nucleation behavior of primary α-Al during solidification and then controlled the spangle size.

Microstructure evolution of a Zn-Al coating co-deposited on low-carbon steel by pack cementation

In this study, Zn–Al coatings were co-deposited on AISI 1020 steel by pack cementation. The as-prepared coatings were characterised by scanning electron microscopy, energy–dispersive X–ray spectroscopy, and X–ray diffraction. The evolution mechanism of the coating was modelled and analysed in detail. Furthermore, the corrosion resistance of the as-received coatings was investigated by a potentiodynamic polarisation test in a 3.5% NaCl solution. We observed that the relatively loose and porous structure of those coatings was a function of the Al content in the packed powders. The regions with a natural porous structure evidently increase with an increase in Al concentration. The Zn-rich layer was formed because of the dominant inward diffusion of Zn with a small diffusion of Fe in the substrate. Thus, the Zn-rich layer/substrate interface moved into the ferrous substrate. As the reaction continued, the deposition of Al dominated. The interdiffusion of Al and Zn in the Zn-rich layer and the diffusion of Fe into the Zn-rich layer towards the Al-rich layer led to the nucleation and growth of the Fe–Al phases and the consumption of the Zn-rich layer. As a consequence, the Al-rich layer/Zn-rich layer interface moved inside the Zn-rich layer. At higher deposition temperatures, when the heat was released because of the Fe–Al phase formation, the evaporation of Zn resulted in void formation in the Al-rich layer. The potentiodynamic polarisation test results show that both Zn and Zn–Al coatings significantly enhance the corrosion resistance of a ferrous substrate, but Zn–Al coatings seem to be more efficient.

Evaluation of the Performance of Galvanized Steel Support in Construction of Living Wall Systems

Currently, Living Wall Systems (LWSs) are assuming great importance in the built environment, due to environmental and aesthetic advantages, as well as the use of urban residual space and underutilized surfaces of buildings. However, the maintenance and the durability of the materials used have been a challenge for architects and professionals in the field. The aim of this paper is to evaluate the anti-corrosion performance of a steel framing profile, galvanized carbon steel (55% Al-Zn), a sustainable material with easy assembly, to apply LWS in the hot and humid tropical climate of Niteroi (Rio de Janeiro, Brazil). In order to create the conditions of the tests, “X” cut were made in Al-Zn coating, sanding, and application of epoxy and glass fiber-reinforced polyester. After the experiments that lasted four months, the 55% Al-Zn coating was analyzed using Scanning Electron Microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). The results of the tests were promising for the use of this galvanized steel for application as a support for green vertical facades. 55% Al-Zn coatings are recommended for marine atmospheres due to their good anti-corrosion performance.

Corrosion Behavior of Arc-Sprayed Zn-Al Coating in the Presence of Sulfate-Reducing Bacteria in Seawater

Zn-Al coatings were prepared by high-velocity arc spraying process and were sealed by the silicone resin to improve their corrosion resistance. The corrosion behavior of the unsealed and sealed Zn-Al coatings in the presence of sulfate-reducing bacteria (SRB) in seawater was evaluated, and the related mechanism was discussed. The results showed that the charge transfer resistance value of the sealed coating was almost ten times higher than that of the unsealed coating, and the concentration of element S in the covering layer of the former was half lower than that of the latter. The corrosion resistance of the coating was apparently improved by the sealing treatment. The corrosion rate of the coatings first increased and then decreased during the immersion time of 8 days in the seawater with SRB. The removal of the passive films in the initial period was attributed to penetration of the corrosion medium into the coating and the dissolution of the active zones inside the coating. The adhesion of SRB and accumulation of corrosion products on the coating surface would protect the coating from being further damaged.

Preparation and Properties of Superhydrophobizted Sprayed Zn-Al Coating

A superhydrophobic ZnAl coating was prepared by the electric arc spraying technology and then surface modification by stearic acid/ethanol. The surface wettability, morphology and chemical structure of the ZnAl coating before and after modification were characterized by contact angle measurement(OCA-20), scanning electron microscope(SEM) and artificial FTIR spectrometer(ATR), respectively. The impedance spectrum and polarization curves of the coatings were measuared by electrochemical workstation(Solartron Analytical) with three electrodes system. The results show that the as sprayed ZnAl coating consists of irregular micro-and nano-sized alloy particles and pores, and exhibits clear hydrophilicity, which may be ascribed to the high surface energy of metallic coating. After the surface modification with stearic acid, the static contact angle of the coating reached 153.8° with a rolling angle less than 10°, because there exsited a large number of hydrophobic long alkyl chains on the surface of the modified Zn Al coating. In addition, the surface modification could significantly enhance the corrosion resistance of ZnAl coating due to that the thin hydrophobic film plays an important role in supression of the fall off and dissolution of corrosion products on the ZnAl coating, leading to the increase of charge transfer resistance and the corrosion current density.

Evolution of the surface chemistry of hot dip galvanized Zn–Mg–Al and Zn coatings on steel during short term exposure to sodium chloride containing environments

In the current study, the evolution of corrosion products on the surfaces of hot-dip galvanized Zn–Mg–Al and standard Zn coatings during short term exposure to standardized salt spray test was investigated by X-ray photoelectron spectroscopy. The obtained results demonstrated a rapid formation of double layered hydroxides (DLH) covering the surface of the Zn–Mg–Al coatings. The DLH surface layer was found to stabilize the surface pH and hinder further surface alkalization as observed for the Zn coatings and indicated by the occurrence of Na2CO3. As a consequence, the progress of Zn–Mg–Al corrosion was slowed down, but not completely stopped.

Corrosion of wire arc sprayed ZnMgAl

In the past 10 years, hot-dip-galvanized ZnMgAl coatings containing 1–2 wt% of Mg and Al each and a Zn base have demonstrated their superior corrosion resistance compared to ZnAl coatings. However, applications of ZnMgAl coatings have been limited to continuous strip galvanizing so far. In this paper, a cored wire for arc spraying of ZnMgAl was developed and the resulting coating was compared to wire arc sprayed Zn and ZnAl15 coatings. The coatings were exposed to the neutral salt spray test for up to 2448 h and the corrosion products were characterized using optical microscopy, EPMA and XRD. ZnMgAl showed superior corrosion resistance compared to ZnAl15 and Zn due to the formation of layered double hydroxides (LDH) and delaying the formation of hydrozincite as a result of the formation of MgCO3.

Long-term atmospheric corrosion properties of thermally sprayed Zn, Al and Zn–Al coatings exposed in a coastal area

Abstract The long-term atmospheric corrosion properties of thermally sprayed Zn, Al and Zn–Al coatings have been evaluated using an electrochemical impedance measurement and several analytical techniques. All the thermal-sprayed specimens with 100 μm coating thickness have protected the steel substrates. In case of the Zn–Al coating, the red rust was not observed regardless of the coating thickness. The corrosion products were identified by the XRD analysis. Preferential dissolution of zinc was observed on the Zn–Al coating by EPMA analysis. The electrochemical impedance results provided an insight about the surface structures of each thermally sprayed coating.

Influence of metallurgical states on the corrosion behaviour of Al–Zn PVD coatings in saline solution

The objective of this study is to define the corrosion behaviour of different Al–Zn coatings, deposited by magnetron sputtering. The coatings exhibiting the best corrosion resistance are then characterised during long immersion tests in neutral 5wt.% NaCl solution.The results show that the corrosion behaviour is strongly dependent on the zinc content. The evolution of the degradation mechanism is also related to the microstructure of the alloys. These alloys present very interesting properties for steel protection. Nevertheless, the zinc content has to be well defined in order to avoid a high dissolution of the coating.