Sacrificial Corrosion Protection Research Articles

Effect of Proportions of Γ and Iron–Zinc Solid Solution Phases on the Corrosion Prevention Performance of Mixed Coating Layers on Heated Galvannealed Steel Sheets

Coating layers having different ratios of a Γ phase to an Fe–Zn solid solution phase were produced on galvannealed steel sheets by heat treatment. The corrosion prevention characteristics of these layers were then investigated using combined cyclic corrosion test, electrochemical measurements and analyses of corrosion products. A coating layer with a larger proportion of the Γ phase showed better corrosion prevention properties along with a smaller corrosion mass loss. The Γ phase exhibited a sacrificial corrosion protection effect with regard to both the Fe–Zn solid solution and the steel substrate while the Fe–Zn solid solution showed a sacrificial corrosion protection effect on the steel substrate. The corrosion products formed from the Γ phase comprised Zn5(OH)8Cl2·H2O, Zn5(CO3)2(OH)6, ZnO and various amorphous compounds, while the Fe–Zn solid solution generated Zn-containing ferrihydrite and amorphous compounds. The presence of Zn evidently stabilized the ferrihydrite and delayed the formation of crystalline iron oxyhydroxide based on comparisons with corrosion products formed on cold-rolled steel sheets. These effects improved the corrosion prevention performance of the Fe–Zn solid solution. The zinc-based corrosion products formed from the Γ phase provided even better corrosion prevention performance by delaying the formation of crystalline iron oxyhydroxide and were also themselves resistant to reduction.

(Digital Presentation) The Role of Mg in Cut-Edge Corrosion Protection of 55 Mass% Al-Zn-Mg Coated Steel Under a Wet-Dry Cyclic Condition

Pre-painted hot-dip 55 mass% Al-Zn coated steel sheets are widely used as a building material due to their superior corrosion resistance. In consideration of its long-term service, a pre-painted hot-dip 55 mass% Al-Zn-2 mass% Mg coated steel sheet with enhanced corrosion resistance has been developed in recent years.1 It has been shown that the addition of 2 mass% Mg not only reduced the corrosion rate by 1/3 but also inhibited the delamination of organic paints from the cut-edge. As yet, however, the role of Mg in the cut-edge corrosion protection of the 55 mass% Al-Zn-2 mass% Mg coated steel has not been completely clear. In this study, we focused on the influence of Mg-containing corrosion products on the electrochemical properties of the coating layer and the steel substrate. Hot-dip 55 mass% Al-Zn-2 mass% Mg-1.6 mass% Si and 55 mass% Al-Zn-1.6 mass% Si coated steel sheets were used in this study. The Al-Zn-Mg coating layer is composed of Al-rich, Zn-rich, and Mg-Si phases. Our previous study has reported that for the Al-Zn-Mg coating layer, the Zn-rich phase preferentially dissolves during the initial process of cut-edge corrosion.2 In addition, Mg also preferentially dissolves from the Mg-Si phase in the Al-Zn-Mg coating layer. The wet and dry cyclic corrosion test showed that the formation of the Zn-based corrosion products at the cut-edge for the Al-Zn-Mg coated steel was more inhibited than that for the Al-Zn coated steel. In addition, the sacrificial corrosion protection ability of the Al-Zn-Mg coated steel was higher than the Al-Zn coated steel. It was found that the dense corrosion products including Mg were formed on the steel substrate at the cut-edge for the Al-Zn-Mg coated steel 1 hour after the onset of the corrosion test. The Mg-containing corrosion products slightly reduced the cathodic current for the oxygen reduction reaction, and this is thought to be one of the factors for the improved cut-edge corrosion resistance.1) N. Shimoda, Y. Morimoto, Y. Kubo, S. Fujii, and S. Shiragaki, Galvatech 2015 Proceedings, 802 (2015).2) S. Tokuda, I. Muto, Y. Sugawara, M. Takahashi, M Matsumoto, and N. Hara, Corros. Sci, 129, 126 (2017).

Sacrificial Corrosion Protection Ability of Al, Al-Mg, and Al-Si Thermal Spray Coatings and Corrosion Resistance for the Defect Part of the Coatings

Sacrificial Corrosion Protection Ability of Al, Al-Mg, and Al-Si Thermal Spray Coatings and Corrosion Resistance for the Defect Part of the Coatings

Friction transitions and connections to third bodies for a Cd coating on steel substrate

Cd coating is used in aerospace industries from last five decades due to its sacrificial protection and lubrication properties. Although Cd coating is primarily used due to its sacrificial corrosion protection when applied on steel substrate, the added benefit of modifying the tribological behavior by acting as a lubricious layer gives it a leading-edge than other coatings. Often the measurement of friction coefficient (CoF) is reported as a value generated after full sliding cycle. This measurement of average CoF generally limits the study of local variation in CoF occurring within one sliding cycle, which can be significantly different with change in spatial position due to change in third body morphology. In this study, a linearly reciprocating sliding test is used to measure the CoF at a sampling rate of 800 Hz along the track length to generate triboscopic image with steel countersphere. The instantaneous CoF obtained with triboscopy is correlated with the wear track morphology using scanning electron microscope (SEM) and optical profilometer for variation in contact conditions. Tribological test performed in dry atmosphere shows an average CoF of 0.4 till the end of the test whereas with increase in relative humidity to 60%, the average CoF changes from 0.4 to 0.8 at the end of the test due to change in contact conditions. Soft Cd coating on low carbon steel substrate is used to study these variations in third body morphology.

On the miniaturised sacrificial protection achieved by surface precipitation in aluminium alloys

Metal rich primers comprising of zinc (Zn) or magnesium (Mg) particles are applied onto certain aluminium (Al) alloys to sacrificially protect the alloys. An alternative method to sacrificially protect Al alloys is to induce the formation of a homogeneous distribution of anodic surface precipitates upon them. In this contribution, surface precipitation is exploited to impart sacrificial corrosion protection to Al alloys. Metallurgical thermal treatments were performed to form anodic surface precipitates (MgZn2, Al2MgCu and Mg2Si) on two commercial Al alloys: AA7050 and AA6061. Corrosion tests demonstrate that these miniature surface precipitates formed upon Al alloys can impart sacrificial cathodic protection.

Sacrificial effect of titanium powder on the corrosion by hydrogen fluoride in LiF-NaF-KF

Sacrificial corrosion protection, a new use of Ti powder in molten salt blankets, is proposed. Redox reactions of mixed Ti powder into molten fluoride salts are predicted to suppress the TF corrosion of structural materials. Stainless Steel 430 (SS430) is immersed into FLiNaK containing HF at 823 K for 6 h. Before the immersion, the Ti powder either exposed to air or not exposed to air at all is mixed into FLiNaK. It has been found that either types of mixed Ti powder can suppress the HF corrosion of SS430.

Electrodeposition of manganese layers from sustainable sulfate based electrolytes

Functional manganese-(Mn)-containing layers are becoming increasingly important in the fields of sacrificial corrosion protection, biodegradable medical devices or electrochemical energy conversion systems. Electrodeposition can be a low cost and time-efficient production route, but the very electronegative nature of Mn makes this reduction process quite challenging.In this paper, electrolytic potentiostatic deposition of metallic Mn layers from environmentally friendly aqueous manganese sulfate electrolytes with pH3 is successfully demonstrated. A continuous electrolyte flow in the cathodic compartment of the electrochemical cell for controlling the pH value during deposition was found to be essential for achieving good layer qualities. Based on cyclic voltammetry analysis in combination with quartz crystal microbalance measurements a suitable deposition potential range was identified. The obtained electrodeposited layers were characterized by means of SEM, XRD, GD-OES and XPS. The shift of the deposition potential from −2.4 VMSE to −2.6 VMSE (deposition time 60min) yields a thickness increase of the metallic α-Mn deposits from <500nm to ~2μm. Only thin additional surface regions of Mn-oxides/-hydroxides were identified. The important role of (NH4)2SO4 as complex-forming electrolyte additive is discussed and an impact of the salt concentration on the deposit properties is revealed. This is a promising starting point for further Mn alloy deposition analysis.

Micro-electrochemical investigation on the role of Mg in sacrificial corrosion protection of 55mass%Al-Zn-Mg coated steel

The effects of Mg on the anodic dissolution behavior of the 55mass%Al-Zn coating layer were determined by in situ observation during galvanostatic polarization. The Zn-‍rich phases were observed to corrode at lower potentials than the dissolution potential region of the Al-rich matrix phases, and the dissolution duration of the Zn-rich phases was prolonged by Mg addition. Moreover, the corrosion products of the 55mass%Al-Zn-Mg coating layer were suggested to inhibit the oxygen reduction reaction on the steel substrate. The sacrificial corrosion protection mechanisms due to the addition of Mg to the 55mass%Al-‍Zn coating layer were discussed.

Electrodeposition of ternary Zn–Ni–Sn alloys from an ionic liquid based on choline chloride and their characterisation

Ternary Zn–Ni–Sn alloy coatings with a range of compositions were potentiostatically electrodeposited on steel substrates from a deep eutectic solvent-based electrolyte. The effect of electrodeposition potential on the morphology, chemical and phase compositions, and corrosion behaviour of the deposits was analysed. The co-deposition mechanism of Zn–Ni–Sn alloys was found to be normal whereby increasing the electrodeposition potential enhanced the ternary alloy Zn content (active element) and greatly suppressed the alloy Sn and Ni content (noble elements). The X-ray diffraction phase analyses showed that Ni in the deposits exists in the form of metal compounds including β-Ni3Sn2 as well as γ-NiZn3. The improved corrosion resistance observed in all ternary alloys was attributed to their compact morphology, phase content and chemical composition. Comparison of corrosion performances shows that ternary Zn–Ni–Sn alloys are superior for sacrificial corrosion protection of steel metallic substrates compared to binary Zn–Sn and Zn–Ni alloys.

Electrodeposition, Microstructural Characterization and Anticorrosive Properties of Zn-Mn Alloy Coatings

Zinc alloy coatings are widely used for sacrificial corrosion protection of ferrous materials, in particular in the automotive industry. Zinc-Manganese (Zn-Mn) alloys were reported by Boshkov et al. to provide higher corrosion protection than pure zinc coatings due to a double protective effect involving corrosion products with low dissolution rates as well as higher cathodic protection than pure zinc due to the use of Mn [1-5]. In the framework of this work, various chloride baths with and without additives were investigated by means of voltammetric and Electrochemical Quartz Crystal Microbalance (EQCM) studies in order to define optimal deposition parameters such as deposition potential, plating bath composition and additives in regards with the Mn content in the final coatings. The composition, morphology and crystallographic structure of the coatings were studied using Atomic Absorption Spectroscopy (AAS), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-ray diffraction (XRD). The aim of this study is to obtain compact, smooth and monophasic Zn-Mn alloy coatings with a high Mn content. A transition from 11 wt.% Mn to 17 wt.% Mn was observed in the case of coatings deposited in presence of additives. Coatings deposited from the additive free electrolyte were rough with a dendritic morphology. By contrast, the 17 µm-thick coatings obtained from the bath with additives consisted of a compact and smooth monophasic single ε-Zn-Mn hexagonal close-packed (HCP) phase with a highly textured crystallography along the <110> direction. The corrosion behavior of the Zn-Mn alloys and pure zinc deposits was investigated by means of potentiodynamic polarization curves and polarization resistance (Rp) measurements. Higher corrosion protection was obtained for coatings deposited in presence of additives compared to pure Zn coatings. Zn-Mn coatings deposited in absence of additives found to provide lower protective ability than Zn coatings. The results clearly show that the alloying of Zn with Mn is not a sufficient condition to provide higher corrosion protection than that of pure zinc layers. In fact, coating morphology and crystallographic orientation have a significant influence on the anticorrosive properties of Zn-Mn alloys. 1. Boshkov, N., et al., Galvanic alloys Zn–Mn—composition of the corrosion products and their protective ability in sulfate containing medium. Surface and Coatings Technology, 2005. 194(2-3): p. 276-282. 2. Boshkov, N., S. Vitkova, and K. Petrov, Corrosion Products of Zinc-Manganese Coatings: Part I - Investigations Using Microprobe Analysis and X-Ray Diffraction. Metal Finishing, 2001. 99(9): p. 56-60. 3. Boshkov, N., Galvanic Zn–Mn alloys—electrodeposition, phase composition, corrosion behaviour and protective ability. Surface and Coatings Technology, 2003. 172(2-3): p. 217-226. 4. Boshkov, N., et al., Influence of the alloying component on the protective ability of some zinc galvanic coatings. Electrochimica Acta, 2005. 51(1): p. 77-84. 5. Boshkov, N., K. Petrov, and G. Raichevski, Corrosion behavior and protective ability of multilayer Galvanic coatings of Zn and Zn–Mn alloys in sulfate containing medium. Surface and Coatings Technology, 2006. 200(20-21): p. 5995-6001.

Effect of Phosphate and Chromate Pigments on Sacrificial Corrosion Protection by Al–Zn Coating and Delamination Mechanism of Pre-painted Galvalume Steel

Effect of Phosphate and Chromate Pigments on Sacrificial Corrosion Protection by Al–Zn Coating and Delamination Mechanism of Pre-painted Galvalume Steel

Electrochemical Roles of Anti-corrosive Pigments in Sacrificial Corrosion Protection of Painted Galvanized Steel and their Relation to Organic Coating Delamination

The effect of anti-corrosive pigments on the delamination of an organic film on a Zn coated steel was investigated using a cyclic wet-dry corrosion test (according to ISO 16539 Method A). The organic film was made from a mixture of polyvinyl butyral-co-vinyl acetate (PVB) ethanol, and a pigment. SrCrO4 or Na2HPO4 was added as a pigment. The delaminated area around a deep scratch on the specimen with the SrCrO4-containing film was smaller than those of the Na2HPO4-containing and pigment-free films. The corrosion rate and potential of the Zn layer coupled with the steel were estimated on the basis of the iR-drop in the films and the polarization curves of the Zn and steel electrodes. Also, the electrode potentials of the Zn under the PVB films were measured by scanning Kelvin probe force microscopy. From these results, it was confirmed that the delamination of the PVB films on galvanized steels was mainly caused by the anodic reaction of the Zn layer. The galvanic coupling of the delamination fronts at the interface of the Zn layer and the PVB film to the steel substrate at the scratches, inhibits the oxygen reduction reaction on the steel, in effect preventing Zn corrosion.

Electrodeposition of Zn-Mn coatings on steel from 1-ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl) imide ionic liquid

This work studies the electrodeposition of Zn-Mn alloy on high-resistance steel substrates from 1-ethyl-3-methylimidazolium-bis (trifluoromethanesulfonyl) imide ionic liquid and Zn and Mn bis (trifluoromethanesulfonyl) imide salts and their sacrificial corrosion protection properties. The cleaning of the electrodeposited Zn-Mn alloy for the purpose of removing any ionic liquid remains has proved to be a fundamental step. A variety of solvents were tested, showing that the best results were obtained with dichloromethane (CH2Cl2) since this solvent removed the ionic liquid residues without reacting with the electrodeposited coating. The Zn/Mn ratio in the electrodeposited material is dependent on the concentration of the solution salt, as well as on the potential chosen for electrodeposition. The most promising Zn-Mn alloy was electrodeposited from 0.15M Zn to 0.3M Mn salt solution at −1.8V. The electrodeposited coating under these conditions shows a shift in the corrosion potential towards nobler values due to the Mn incorporation in the alloy, and has sacrificial properties that show lower dissolution rates than Zn when galvanic coupled with steel with an area ratio of 1:1.

Suppressing Dendrite Growth during Zinc Electrodeposition by PEG-200 Additive

Electrodeposition of zinc at current densities close to the mass transport limit produces needle-like dendrites. Suppressing dendrites is of technological interest to applications in sacrificial corrosion protection coatings and flow batteries. In the present work, we report the use of polyethylene glycol (PEG, M.W. = 200) as an effective electrolyte additive to suppress dendrites during zinc electrodeposition from halide-based electrolytes. Dendrite growth rate is measured as a function of the PEG concentration using in situ optical microscopy, which shows that the dendrite suppression efficacy due to PEG increases with PEG concentration. Polarization experiments on a rotating disk electrode provide system parameters, i.e., the exchange current density and the cathodic transfer coefficient, which confirm that PEG suppresses the zinc electrodeposition kinetics. The kinetic parameters are incorporated into a simple electrochemical model for activation-controlled dendrite propagation. The model predicts an order of magnitude reduction in the zinc dendrite growth rates in the presence of high concentration of PEG (10000 ppm), consistent with experimental findings.

Comparison of the intrinsic properties of EBPVD Al–Ti and Al–Mg coatings

Aluminium based alloys were deposited on glass slide substrates by electron-beam evaporative PVD (EBPVD) technique in order to assess to the intrinsic corrosion behaviour in saline solution. Alloying elements (Ti or Mg) were added in order to improve both mechanical and corrosion behaviours of aluminium films. The goal of this study is to develop new alternative sacrificial coatings that could protect steel flat products against corrosion with enhanced mechanical properties in order to limit the seizing sensitivity. Because of the difference in vapour pressures, aluminium and alloying elements were co-evaporated from two separate sources. Mixing of the vapour flux was the most appropriate experimental method to ensure a homogeneous distribution of the alloying element into the aluminium based coating. Different contents of transition metals were examined, and it was noticed that the microstructure evolves from a supersaturated solid solution to an amorphous phase due to the lattice distortions with the incorporation of the alloying elements. Electrochemical behaviour of the EBPVD coatings in saline solution was investigated. It is shown that aluminium can be mechanically reinforced while preserving sacrificial corrosion protection properties. The evolution of the properties was found to be strongly linked to the nature of the incorporated element. A comparison with a previous study on the electrochemical and mechanical behaviour of EBPVD Al–Cr and Al–Gd coatings permitted a comprehensive analysis of the influence of the incorporation of transition metals in aluminium.

Scanning Kelvin Probe Analysis of Cut Edge Corrosion on Prepainted Galvanized Steel with Chromate-Containing Epoxy Primer

Prepainted galvanized steels with chromate-containing and chromate-free primers were prepared to understand the effect of the chromate on cut edge corrosion. The initiation and growth of red rust were investigated with the combination of scanning Kelvin probe techniques and cyclic wet-dry corrosion tests. Chromate was proved to inhibit oxygen reduction reaction on the steel substrate, providing the situation in which the Zn layer readily acts as a sacrificial anode. Even under a thin electrolyte layer of 70 μm, the corrosion potential of cut edge for the chromate-containing specimen was found to be almost the same as that of zinc. In the case of the chromate-free specimen, however, the corrosion potential increased with decreasing thickness of the electrolyte layer to 70 μm, which indicates sacrificial corrosion protection of the Zn layer is no longer effective under thin electrolyte layers. It was also expected that chromate enhances the ability of red rust to prevent the anodic dissolution of the steel substrate.

Assessment of the corrosion protection of aluminium substrates by a Mg-rich primer: EIS, SVET and SECM study

Magnesium-rich coatings have the capability of providing sacrificial corrosion protection to aluminium substrates and therefore present a new and challenging field of development. In this work the mechanism of protection of an aluminium substrate by a Mg-rich coating was investigated using the scanning vibrating electrode technique (SVET) and scanning electrochemical microscopy (SECM). The SVET has shown the evolution of the pit activity with time under sacrificial protection, whereas the SECM allowed indirect sensing of the cathodic activity above the electrodes. The study was complemented by classical electrochemical techniques, namely electrochemical impedance spectroscopy and open circuit potential measurement. The results show that magnesium acts in a first stage by both preventing nucleation of pits and inhibiting the growth of the already existing ones, whereas at a later stage the precipitation of a porous layer of magnesium oxide at defective areas leads to some degree of barrier protection.

Characteristics and Verification of a Low Hydrogen Embrittling Zinc-Nickel Electroplate, Developed for Corrosion Protection of High Strength Steels

SUMMARYA coating process is outlined that gives low hydrogen embrittling zinc-nickel binary alloy electroplate for sacrificial corrosion protection of high strength steels, and the physical properties of the coatings produced are presented. The highly corrosion resistant zinc-nickel binary alloy coatings produced by the new process comply fully with the ASTM test requirements for control of hydrogen embrittlement. They are an alternative to the cadmium coatings currently employed for the corrosion protection of high strength steels. The results of hydrogen embrittlement tests and of structural analyses are discussed in light of the structure of the zinc-nickel coating, and of its efficiency in allowing labile hydrogen to diffuse out of the coated high strength steels.

Tribology and corrosion of Al-1.5wt.%Zn-5wt.%Sn ion platings

Al-Zn alloy coatings are superior to aluminium coatings in providing better galvanic corrosion resistance to steel components. In many applications, both good sacrificial corrosion protection and tribological properties are in question. In this work an attempt to improve the frictional characteristics of Al-1.5wt.%Zn alloy ion platings through introducing a small amount (5 wt.%) of a solid lubricant such as tin has been carried out. Tribological tests have shown a considerable improvement in the frictional behaviour caused by the microstructure of the Al-1.5wt.%Zn-5wt.%Sn alloy coatings which consists of an aluminium-rich phase surrounded by a continuous matrix of tin-rich phase. Corrosion tests have shown, however, a deteriorating effect on the corrosion tendency and corrosion rate of Al-1.5wt.%Zn coatings when tin is introduced into them.

Al-Zn coatings for the corrosion protection of steel

Aluminum coatings have been reported to be the most suitable for replacing toxic cadmium for the protection of steel and titanium alloys against corrosion. The relatively poor galvanic corrosion protection of aluminium coatings, however, has led to a search for a more effective coating. To this end, pure aluminium and controlled-composition Al-Zn alloy coatings were ion plated onto steel substrates. Over a range of coating conditions the aluminium and the Al-Zn alloy coatings have very similar columnar structures. They were equally successful in protecting the underlying steel. However, a simulation of the coating damage by masking the steel substrate during plating showed the galvanic corrosion protection of Al-2.5%Zn alloy coatings to be superior to that of aluminium. It is probable that this very effective sacrificial corrosion protection means that the structure of the coating is relatively unimportant and that excellent galvanic corrosion protection can be provided by low density columnar structure coatings of Al-Zn alloys.