Hot-dip Galvanized Steel Surfaces Research Articles

Biopolymeric Anticorrosion Coatings from Cellulose Nanofibrils and Colloidal Lignin Particles.

This study presents a process for preparation of cellulose–lignin barrier coatings for hot-dip galvanized (HDG) steel by aqueous electrophoretic deposition. Initially, a solution of softwood kraft lignin and diethylene glycol monobutyl ether was used to prepare an aqueous dispersion of colloidal lignin particles (CLPs) via solvent exchange. Analysis of the dispersion showed that it comprised submicron particles (D = 146 nm) with spherical morphologies and colloidal stability (ζ-potential = −40 mV). Following successful formation, the CLP dispersion was mixed with a suspension of TEMPO-oxidized cellulose nanofibers (TOCN, 1 and 2 g·L–1) at a fixed volumetric ratio (1:1, TOCN–CLPs), and biopolymers were deposited onto HDG steel surfaces at different potentials (0.5 and 3 V). The effects of these variables on coating formation, dry adhesion, and electrochemical properties (3.5% NaCl) were investigated. The scanning electron microscopy results showed that coalescence of CLPs occurs during the drying of composite coatings, resulting in formation of a barrier layer on HDG steel. The scanning vibrating electrode technique results demonstrated that the TOCN–CLP layers reduced the penetration of the electrolyte (3.5% NaCl) to the metal–coating interface for at least 48 h of immersion, with a more prolonged barrier performance for 3 V-deposited coatings. Additional electrochemical impedance spectroscopy studies showed that all four coatings provided increased levels of charge transfer resistance (Rct)—compared to bare HDG steel—although coatings deposited at a higher potential (3 V) and a higher TOCN concentration provided the maximum charge transfer resistance after 15 days of immersion (13.7 cf. 0.2 kΩ·cm2 for HDG steel). Overall, these results highlight the potential of TOCN–CLP biopolymeric composites as a basis for sustainable corrosion protection coatings.

Multiscale and Multi-Technical Approach to Characterize the Hot-Dip Galvanized Steel Surface and Its Consequence(s) on Paint Adhesion and Tendency to Blistering

It is well known that the surface state (cleanliness, composition) of galvanized steel prior to the application of an organic coating is an important parameter. The surface state will affect the adhesion properties of the complete system and therefore will also impact its corrosion resistance and its tendency to blistering. Before the application of a pretreatment layer, galvanized steel strips are normally alkaline cleaned. This step is known to remove the native oxide film formed on hot dip galvanized steel after processing and appears as one of the most important steps to study the impact of the surface properties on the performance of painted systems. This study focused on making use of the cleaning step to input a variability on the surface composition (mainly surface concentration of aluminum) and evaluate its consequence(s) on the performance of a complete paint system. The results showed that, a variability in terms of surface aluminum concentration could be achieved by the cleaning step and that signs of performance improvement in terms of adhesion and tendency to blistering were spotted with a low content of aluminum at the surface.

Cleaning Optimization of Hot-Dip Galvanized Steel Surfaces in Preparation for Paint Application

Hot-dip galvanized steel surfaces are cleaned, pre-treated with titanium-containing solution and then painted for use. Removal of the alumina layer from galvanized steel surfaces during the cleaning process is essential before effective paint application. Bad adhesion results if the alumina layer is not completely removed, and an insufficient concentration and uneven distribution of titanium oxide is formed across the galvanized surface during pre-treatment. The alkaline cleaner concentration must be optimized to ensure effective removal of the alumina layer. Hot-dip galvanized steel samples were cleaned using typical line conditions and cleaning solutions with varying free alkalinities. The alumina layer was then measured on each sample by glow-discharge optical emission spectroscopy. Thereafter, the samples were treated with titanium-containing pre-treatment solution. The titanium oxide concentration was measured by inductively coupled plasma optical emission spectroscopy. It was found that a free alkalinity of at least 3.2 mEq/L is required to fully remove the alumina layer. The alumina-free samples also gave a titanium oxide layer after pre-treatment within the target concentration of 4–8 mg/cm2. A free alkalinity of 3.5 ml was thereafter implemented commercially: analysis of samples from two galvanizing lines showed no presence of alumina, a uniform titanium oxide distribution across the widths of the line samples and acceptable titanium concentrations.

Self-assembled graphene oxide microcapsules in Pickering emulsions for self-healing waterborne polyurethane coatings

A self-assembly process was employed to prepare the graphene oxide microcapsules (GOMCs), containing linseed oil as the healing agent. The nanometer-thick shells of GOMCs were built by the liquid crystalline assembling of graphene oxide (GO) sheets, forming at liquid–liquid interface in Pickering emulsions. The GOMCs were embedded into waterborne polyurethane matrix, enabling the facile fabrication of self-healing composite coatings on hot-dip galvanized steel surfaces. The inclusion of GOMCs in the composite coatings not only imparted self-healing properties to the coatings, but also improved their anticorrosion properties because of the physical barrier of the GO shell, leading to much better survival to the weather/marine environment and surface wear.

Effect of Hot Dip Galvanized Steel Surface Chemistry and Morphology on Titanium Hexafluoride Pretreatment

Titanium hexafluoride pretreatments are known to improve paint adhesion and function as a barrier between the coating and the hot dip galvanized (HDG) steel surface. Interactions at the zinc/pretreatment interface are of utmost importance for the formation of pretreatment layers and the corrosion resistance of color coated hot dip galvanized steels. Removal rate of inert aluminum oxide from HDG steel samples by chemical dissolution was studied. XPS measurements showed that the surface Al2O3 layer thickness decreased rapidly already at mild alkaline cleaning, while complete removal of Al required severe etching. Low reactivity of an Al2O3-rich surface was confirmed by impaired formation of a titanium hexafluoride pretreatment layer. Grain boundaries and deformation twinnings were shown to be of importance for the reactivity of the HDG surface and for the precipitation of the pretreatment chemical. Helium ion microscopy images and electron probe microanalysis (EPMA) of a pretreated sample showed accumulation of the pretreatment chemical at the grain boundaries. Al removal rate was fast at the deformation twinnings at the grain plateaus. Slow Al removal was observed at dendritic valleys and grain boundaries. The results increase understanding of the reactivity of hot dip galvanized steel surface.

Hybrid sol–gel coatings for corrosion protection of galvanized steel in simulated concrete pore solution

The aim of this experimental research was to study the electrochemical behavior of organic–inorganic hybrid (OIH) coatings for corrosion protection of hot-dip galvanized steel (HDGS) in the first instants of immersion in simulated concrete pore solution (SCPS) (pH > 12.5). The electrochemical performance of the OIH coatings was assessed by electrochemical impedance spectroscopy, potentiodynamic polarization curves, macrocell current density, and polarization resistance. The OIH coatings were prepared via the sol–gel method and were deposited on HDGS surfaces by dip-coating using one or three dip steps. The electrochemical results obtained for HDGS samples coated with OIH matrices in SCPS showed higher corrosion resistance than bare HDGS; as the molecular weight (MW) of Jeffamine® increased the barrier protection of the coating decreased. The lowest protection efficiency was found for HDGS samples synthesized with oligopolymers with an MW of 2000. Coatings produced with an oligopolymer of 230 MW conferred the highest protection. The surface morphology of the OIH coatings deposited on HDGS surfaces was studied by atomic force microscopy. The results show that the roughness of the OIH films depends on the MW of Jeffamine® and on the number of dip-coating steps used. Thermogravimetry results show that the Jeffamine® MW affected the thermal properties of the prepared OIH samples. The prepared OIH materials are thermally stable within the range of 20–80°C.

Ureasilicate Hybrid Coatings for Corrosion Protection of Galvanized Steel in Cementitious Media

This study is focused on the electrochemical behavior and surface analysis of an eco-friendly organic–inorganic hybrid (OIH) coating for hot dip galvanized steel (HDGS) in contact with cementitious media. This treatment is a proposed alternative to replace toxic Cr(VI)-based pre-treatments used to control reactions between the zinc and wet concrete. HDGS samples were coated with two different sets of OIH gels obtained by a sol-gel process using a dip-coating method. Five distinct OIH matrices were obtained by reaction of functionalized metal-alkoxide (3-isocyanatopropyltriethoxysilane) with five different molecular weight diamine-alkylethers. One set of HDGS samples was coated with each of the five pure OIH matrices and another was coated with similar matrices doped with Cr(III). The morphology of OIH coatings over HDGS surface was characterized by SEM/EDS. Similar films were prepared separately and the respective resistivity was measured by electrochemical impedance spectroscopy. Polarization resistance and macrocell current density were used to evaluate the corrosion protection properties of the HDGS coated samples in contact with cementitious media for a period of 74 days. Results showed that the produced coatings provide barrier properties that withstand the high pH of the electrolyte, protecting the HDGS when it first contacts cementitious media.

Characterization by different analytical techniques of SiO2 and silane thin films deposited on rough hot-dip galvanized steel surfaces

The development of thin and environmental friendly coatings on steel surfaces constitutes a major objective of steelmaking industry. Within this objective it becomes necessary to develop analytical approach allowing characterization of so thin coatings on hot dip galvanized substrates in order to control the product quality. XPS, GDOES, SIMS, FTIR and Raman spectroscopies are compared in terms of capability to characterize SiO2-CVD and silane thin films on rough substrates.At the issue of this study, results show that the SiO2 coating of some tens of nm in thickness is continuous and appears to be homogeneous everywhere on the substrate surface. The layers deposited on the materials with sufficiently low roughness have almost similar thickness. In the case of significant surface roughness increase the SiO2 layer becomes thinner.The silane coatings fill up substrate cavities during application and the coating thickness on rougher substrates is significantly higher than on smoother ones. The chemical composition of the silane layers is more uniform for rougher surfaces, whereas on smoother ones the Si concentration gradient is detected in depth.

Effect of SiO2:Na2O molar ratio of sodium silicate on the corrosion resistance of silicate conversion coatings

Passivation treatment by sodium silicate solution is considered as an alternative to chromium chemical conversion treatment to improve the corrosion resistance of hot-dip galvanized (HDG) steels. In this paper, a transparent silicate coating was formed on the surface of HDG steel by immersing in sodium silicate solution with SiO2:Na2O molar ratio in the range from 1.00 to 4.00. The parameter about the SiO2:Na2O molar ratio of silicate solution has been discussed using corrosion resistance and surface morphology. Tafel polarization, electrochemical impedance spectroscopy (EIS) measurements and neutral salt spray (NSS) test show that silicate coatings increase the corrosion resistance of HDG steels. From the results obtained, it is deduced that the optimum SiO2:Na2O molar ratio is 3.50. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction analysis (XRD), and reflectance absorption infrared spectroscopy (RA-IR) show that there are no obvious differences of the chemical composition and structure in various silicate coatings. The silicate coatings mainly consist of zinc oxides/hydroxides, zinc silicate and SiO2. However, atomic force microscopy (AFM) images reveal that the surface of silicate coatings with a molar ratio of 3.50 is more compact and uniform than other silicate coatings.

調質圧延における亜鉛めっき鋼板への表面テクスチャーの転写挙動

Surface texture plays an important role in product quality of steel sheet, which may reduce friction in sheet metal forming and improve paint appearance, especially in the automotive industry. Temper rolling is one of the key processes to determine the surface texture, because it is finally printed by appropriate work-roll surface.However, the printing behavior of surface texture from work-roll to steel sheet are not sufficiently understood, and the qualitative prediction are necessary for higher quality and adequate production operation. The requirements become larger for widely used hot-dip galvanized steel sheet, but the printing behavior has not been clarified.Therefore, the paper is concerned with the printing behaviors of roll surface textures on hot-dip galvanized steel surface in temper rolling. Firstly, the printing behavior is experimentally investigated by using different work-roll surfaces. Then, as representative parameters, average roughness, peak per inch and waviness are characterized. Also, the mutual relations among the parameters are discussed and possible method to predict the surface parameters is proposed and evaluated.

Synergistic corrosion protection for galvanized steel by phosphating and sodium silicate post-sealing

To improve the corrosion resistance of phosphate coatings, the phosphated hot-dip galvanized (HDG) sheets were post-sealed with sodium silicate (water glass) solutions. The morphology and chemical composition of the composite coatings was analyzed using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The effect of sodium silicate post-sealing treatment on the corrosion behaviors of phosphate coatings was investigated by neutral spray salt (NSS) tests and electrochemical measurements. The results show that after the silicate post-treatment the pores among zinc phosphate crystals are sealed with the films containing Si, P, O and Zn, leading to the formation of the continuous composite coatings on the surface of HDG steel. The corrosion resistance of the composite coatings depending on concentration of sodium silicate and post-sealing time is greatly improved by the silicate post-treatment. The optimum concentration of silicate and post-sealing time are 5 g/L and 10 min, respectively. Both the anodic and cathodic processes of zinc corrosion on the samples are suppressed conspicuously, and the synergistic protection effect of the single phosphate coatings and the single silicate films is evident. Moreover, the low frequency inductive loop in electrochemical impedance spectroscopy (EIS) is disappeared and the electrochemical impedance values are increased for more than one order of magnitude. The corrosion protection of the composite coatings is comparable to that provided by the chromic acid post-treatment.

The adhesion of epoxy cataphoretic coating on phosphatized hot-dip galvanized steel

The influence of hot-dip galvanized steel surface pretreatment on the adhesion of epoxy cataphoretic coating was investigated. Phosphate coatings were deposited on hot-dip galvanized steel and the influence of fluoride ions in the phosphating plating bath, as well as the deposition temperature of the plating bath, were investigated. The dry and wet adhesion of epoxy coating were measured by a standard pull-off method. The surface roughness of phosphatized galvanized steel was determined, as well as the wettability of the metal surface by emulsion of the epoxy resin in water. The adhesion of epoxy coatings on phosphatized hot-dip galvanized steel was investigated in 3wt.%NaCI.

Preparing hot-dip galvanized steel surfaces for painting or powder coating: a primer

Supercritical carbon dioxide (scCO2) treatment was employed for rapid formation of a zinc patina layer on hot dip galvanized (HDG) steel. In the presence of H2O and a Cu precursor, an artificial patina consisting of two distinctive phases was formed: a dense ~ 1 μm layer of anhydrous ZnCO3 adjacent to native zinc coating, and a needle-like porous structure showing resemblance to hydrozincite (Zn5(CO3)2(OH)6). The artificial patina layer significantly decreased the surface free energy of HDG, which was evidenced also by good wettability by a polyester melamine coating. Furthermore, the needle-like patina surface structure stayed intact through the coating process, indicating improved coating adhesion. ScCO2 treatment facilitates rapid and impurity-free surface treatment of hot dip galvanized steel, and could be used to tailor novel adhesion and corrosion promoting surface morphologies.