The Influence of Al on the Surface Properties of the Hot-dip Galvanized Melt

Wettability of Zn-Al alloy melt on the pure iron substrate at 450℃was studied.The effect of Al content(Zn,Zn-1Al,Zn-2Al,Zn-3Al,Zn-4Al,and Zn-5Al)on the wetting behavior and interfacial reaction was investigated by high-temperature contact angle measuring device and scanning electron microscope(SEM).The results show that,with the increase of Al content,the initial contact angle of the molten alloy on the substrate decreases gradually and the wettability increases gradually.Compared with the initial contact angle,the final contact angle is slightly reduced,because the Fe-Al inhibition layer is preferentially formed at the interface when adding Al to the alloy.The presence of Al will promote the occurrence of the reactive wetting,leading to an insignificant wetting spreading process,and the final contact angle negligibly differs from the initial contact angle.The adhesion work and charge density distributions of interface systems were calculated based on the first-principles.The results show that the adhesion work of the Fe/Zn and Fe/(Zn-Al)interface model is 2.0171 J/m^(2)and 13.7944 J/m^(2),respectively.The addition of Al greatly increases the adhesion work between alloy melt and iron substrate.Compared with the Zn-Fe and Al-Fe interface models,it can be seen that a significant charge migration phenomenon occurs between the interfaces.The amount of charge migration in the Al-Fe interface model is much larger than that in the Zn-Fe interface model,indicating that the bonding between Al-Fe atoms can occur more easily and the interaction between Al-Fe interfaces is stronger.This is also the reason why the addition of Al increases the adhesion work between interfaces.

Hot-Dip Galvanized Sheet Production and Application

Hot-dip galvanized sheet is wildly used in construction,household appliances,ship,vehicle and vessel building and machinery,etc.In last ten years,with the development of automobile industry,the anti-eorrosion requirements for car body are increasingly strict,by which the rapid development in technology has been promoted.The application of hot-dip galvanized sheet,technological progress in production and some Chinese large units were introduced.

Evolution of appearance profile of hot-dip galvanized car-body steel sheet during deformation process

In recent years, the waterborne free intermediate coating process has been widely used in the automotive industry. Because the baking times and coating thickness are decreased, the surface covering capability of the painting process is reduced, which directly affects the appearance quality（ long-and short-wave values） of the body paint. Thus, there are correspondingly higher requirements for the white body surface profile prior to painting. The surface profile of the white body is mainly affected by the plate material, the surface profile, and the deformation process. So,the change rule for the surface profile during deformation of the steel plate is a key factor in coating appearance optimization. In this paper, we first analyze the typical deformation of the outer cover of a car body. Then ,we examine the change tendency of the surface profile of steel plates with respect to different deformation rates, specifically for a steel plate comprising a hot-dip galvanized bake-hardened steel sheet. Based on our analysis of the influence of the deformation on the coating appearance,we selected 3% ,5% ,and 8% deformation rates in this research. We found the roughness （Ra） value in the typical deformation range （3% -8% ） of the car body to exhibit a decreasing trend at first and then an increasing trend. The Ra value of the 8% deformation is not more than the original plate test value. When the Pc value of the original plate is in the lower range （ about 60）, it exhibits a slight increasing trend in the deformation process （3 % -8 % ）. And when the Pc value of the original plate is in the higher range （ about 120 ）, it exhibits no increasing trend in the deformation process （ 3% -8% ）. In contrast,the waviness （WCA） value in the car body＇s typical deformation range （3%-8%） shows a significant growth trend.

Development of Cr-free anti-fingerprint hot-dip galvanized sheet for household appliances

China has become the maximum household appliances manufacturing base worldwide.It is a new challenge facing the steel industry to develop the low-cost and environment-friendly sheet for household appliance industry,so Cr-free anti-fingerprint hot-dip galvanized sheet for household appliances is the upgraded product which satisfies the requirement of China household appliance industry' s nuisanceless treatment.The paper discusses the technical key points of development on Cr-free anti-fingerprint galvanized sheet for household appliances,including the development of the Cr-free anti-fingerprint chemical and the production technology of Cr-free anti-fingerprint galvanized sheet for household appliances.The paper elaborates the main compositions,physical features and properties of the Cr-free anti-fingerprint chemical, surface quality control technology,anti-fingerprint coating quality control technology,influence of anti-fingerprint film weight on corrosion resistance,conductibility,high-temperature discolouration resistance,acid resistance,alkaline resistance and solvent resistance of Cr-free anti-fingerprint hot-dip galvanized sheet, influence of anti-fingerprint coating uniformity on paintability of the sheet,influence of strip surface roughness on corrosion resistance and conductivity of the sheet and influence of strip surface quality on corrosion resistance of the sheet.Adopting the suitable Cr-free anti-fingerprint chemical and the reasonable production process parameters,the properties of the Cr-free anti-fingerprint hot-dip galvanized sheet conform to the delivery technical norms and the Cr-free anti-fingerprint hot-dip galvanized sheet becomes the new material for household appliances such as computer case.

Growth and corrosion behavior of rare earth film on hot-dip galvanized steel

Hot-dip galvanized(HDG)steel sheets were treated for 30 s?24 h by the rare earth aqueous solution containing 20 g/L Ce(NO3)3·6H2O,and the growth behavior and corrosion resistance of the rare earth film were investigated by SEM,EDS,AES and NSS.The results reveal that the rare earth film becomes thick while the mass gain of the samples does not distinctly change due to the zinc dissolution with the increase of treatment time.The film grows up more quickly and is apt to cracking in the vicinity of zinc grain boundaries,and eventually the film partly warps and flakes off with increasing film thickness.The NSS results show that the corrosion resistance of the film is dominated by both the film thickness and the cracks.With increasing treatment time,the corrosion resistance of the film increases within 1 h due to the increased film thickness and decreases after 1 h because the cracking and flaking off gradually become dominant factor.

Effect of hot-dip galvanizing processes on the microstructure and mechanical properties of 600-MPa hot-dip galvanized dual-phase steel

A C–Mn dual-phase steel was soaked at 800°C for 90 s and then either rapidly cooled to 450°C and held for 30 s(process A) or rapidly cooled to 350°C and then reheated to 450°C(process B) to simulate the hot-dip galvanizing process. The influence of the hot-dip galvanizing process on the microstructure and mechanical properties of 600-MPa hot-dip galvanized dual-phase steel(DP600) was investigated using optical microscopy, scanning electron microscopy(SEM), transmission electron microscopy(TEM), and tensile tests. The results showed that, in the case of process A, the microstructure of DP600 was composed of ferrite, martensite, and a small amount of bainite. The granular bainite was formed in the hot-dip galvanizing stage, and martensite islands were formed in the final cooling stage after hot-dip galvanizing. By contrast, in the case of process B, the microstructure of the DP600 was composed of ferrite, martensite, bainite, and cementite. In addition, compared with the yield strength(YS) of the DP600 annealed by process A, that for the DP600 annealed by process B increased by approximately 50 MPa because of the tempering of the martensite formed during rapid cooling. The work-hardening coefficient(n value) of the DP600 steel annealed by process B clearly decreased because the increase of the YS affected the computation result for the n value. However, the ultimate tensile strength(UTS) and elongation(A80) of the DP600 annealed by process B exhibited less variation compared with those of the DP600 annealed by process A. Therefore, DP600 with excellent comprehensive mechanical properties(YS = 362 MPa, UTS = 638 MPa, A_(80) = 24.3%, n = 0.17) was obtained via process A.

Corrosion behavior and mechanism of the automotive hot-dip galvanized steel with alkaline mud adhesion

The corrosion behavior and mechanism of hot-dip galvanized steel and interstitial-free （IF） substrate with alkaline mud adhesion were investigated by scanning electron microscopy （SEM）, X-ray diffraction （XRD）, electrochemical impedance spectroscopy （EIS）, and linear polarization. The results show that non-uniform corrosion occurs on the galvanized steel and IF substrate during 250 h with the mud adhesion. The corrosion products on the galvanized steel are very loose and porous, which are mainly ZnO, Zn5（OH）8C12·H2O and Zn（OH）2, and Fe-Zn alloy layer with a lower corrosion rate is exposed on the galvanized steel surface; however, the corrosion products on IF substrate are considerably harder and denser, whose compositions of rust are mainly FeOOH and Fe3O4, and several pits appear on their surface. The results of continuous EIS and linear polarization measurements exhibit a corrosion mechanism, that is, under activation control, the charge transfer resistances present different tendencies between the galvanized steel and IF substrate; in addition, the evolution of linear polarization resistances is similar to that of charge transfer resistances. The higher contents of dissolved oxygen and Cl^- ions in the mud play an important role in accelerating the corrosion.

Analysis of causes and influence factors of small black spot defects in hot-dip galvanized pure Zn products

In this study,the factors affecting the formation of small black spot defects on the surface of a hot-dip galvanized pure zinc strip are analyzed. These defects are primarily formed w hen the iron-aluminum inhibition layer is incompletely formed or fails to form or when foreign matter adheres to the surface or embeds in the zinc layer.The defects can be reduced by controlling the cleanliness and activity of the strip base before coating,regulating the zinc pot process parameters,and ensuring the cleanliness of the passline and workshop.

Anticorrosive Properties of Hot-Dip Galvanized Weathering Steel in Atmospheric Exposure

Hot-dip galvanized steel is one of the most used materials in equipment and metallic structures of the Brazilian electric sector. Although carbon steel is the main substrate in the galvanizing hot-dip process, recently, weathering steel has been used as an alternative material to be galvanized. In the transmission line segment of the Brazilian electric sector, for instance, compact towers made of galvanized weathering steel have been installed to conduct energy through urban sites. It is well known that weathering steel, depending on wet and dry cycles and on the pollutants present in the atmosphere, develops a protective patina made of its corrosion products. The patina is dense and strongly adhered to the substrate, blocking the active surface and, thus, reducing the corrosion rate of the base metal. However, when the weathering steel is galvanized, the substrate surface has a layer of zinc and zinc-iron intermetallic alloys. When the sacrificial layer is consumed by atmospheric corrosion, critical questions remain to be answered regarding the underlying substrate. Will the patina of weathering steel be formed? In what condition? Does the hot-dip galvanizing process modify the weathering steel microstructure? The present work carried out an experimental research to shed light on the anticorrosive behavior of hot-dip galvanized weathering steel, after the zinc layer is corroded. This was done by a controlled pickling process, where the zinc layer was removed simulating its consumption during real corrosion processes. The results, obtained through electrochemical techniques and different accelerated corrosion tests, showed that galvanizing weathering steel is a promising technology to enhance the lifetime of structures used in the Brazilian electric sector.

Interpretation on Sebisty effect of hot-dip galvanized steels

Sebisty effect describes the unusual fact that the thickness of the hot-dip galvanizing coating on the steel containing 0.12%0.25% silicon decreases with increasing temperature of zinc bath. The microstructures of hot-dip galvanized coatings on silicon-containing steels (0.14%Si) immersed in zinc bath at 723K and 753K were analyzed. It is found that the thickness of η and ζ layer decreases with the increase of temperature of zinc bath and Г layer changes from discontinuous layer (at 723K) to relatively continuous layer (at 753K). The improvement of the fluidity of zinc bath due to the rising temperature of zinc bath makes η layer thinner. Moreover, the existence of relatively continuous Г layer and the acceleration of the dissolution of ζ layer to zinc bath co-lead to the decrease of the thickness of ζ layer with increasing temperature.

A sandwich-like structure hybrid coating of cold galvanizing coating/polydopamine on hot-dip galvanized steel with enhanced adhesion and corrosion resistance

This study aims to enhance the adhesion strength and anti-corrosion performance of the cold galvanizing coating(CGC)applied on the hot-dip galvanized steel(HDG).Polydopamine(PDA)is deposited on the HDG surface with different time ranges and as an interlayer between CGC and HDG through covalent immobilization.The surface morphology and the covalent interaction between PDA/HDG are exhibited by scanning electron microscope(SEM),atomic force microscopy(AFM)and X-ray photoelectron spectroscopy(XPS).The pull-off adhesion tests before and after neutral slat spry tests show an enhanced dry adhesion strength and less adhesion loss of the hybrid CGC/PDA coated HDG compared with the direct CGC coated HDG.In addition,open circuit potential(OCP)reveals that the corrosion protection performance of the hybrid CGC/PDA coated HDG increases by 200%(up to 201 d)and the corrosion density icorrattaining about 4.45×10^(-7)A/cm^(2).Electrochemical impedance spectroscopy(EIS)measurements and X-ray diffraction(XRD)analysis confirm that the precipitate of the stable chelation formed by PDA and Zn^(2+)between CGC and HDG substrate can also improve the corrosion protection performance.Such a strategy of strengthening adhesion and forming the chelate compound at the HDG surface promises a new route to corrosion protection of CGC on HDG.

Relationship between La and Ce additions on microstructure and corrosion resistance of hot-dip galvanized steel

Scanning electron microscopy,X-ray diffraction,a neutral salt spray test,and electrochemical methods were applied to observe the microstructure and test the corrosion resistance of hot-dip galvanized steel before and after the addition of La and Ce.La/Ce mixture existed in the form of(La,Ce)Zn13 on the coated surface,decreased the coating thickness and accelerated the zinc dendritic growth.The corrosion current density of Zn-0.1La-0.1Ce coating was 63%less than that of pure Zn coating.This phenomenon can be explained that La/Ce mixture inhibited the transformation of Zn5(OH)8Cl2·H2O into Zn5(CO3)2(OH)6 or ZnO,reduced the time for appearance of red rust,and thus enhanced the stability of corrosion products and delayed the oxidation and corrosion processes of galvanized coating.La/Ce mixture improved the corrosion resistance compared to a single La or a single Ce addition.A competitive relationship between La and Ce was observed in the corrosion resistance improvement of hot-dip galvanized steel.

Recent development of UHSS and its hot-dip galvanizing processes in Baosteel

Baosteel has excelled in automotive steel sheets in the past three decades.It has made a significant contribution to the development of China’s automotive industry by producing a wide range of high-quality steel products.Some milestones achieved by Baosteel automotive steel sheet were briefly reviewed.The current challenges in producing ultra-high strength steel(UHSS),especially hot-dip galvanized UHSS,were summarized.The most current advancements in UHSS and the corresponding hot-dip galvanizing processes were discussed.The galvanizability of Si-Mn-added QP steel and DP steel, Mn-added TWIP steel, and Al-added low-density steel has been improved by different techniques in Baosteel.

Accuracy analysis of iron content of galvanized coating using an X-ray fluorescence spectrometer with an L-spectrum

The accuracy(repeatability and reproducibility) of the iron content analysis of galvanized coating using an X-ray fluorescence spectrometer with an L-spectrum is not better than that of flame atomic absorption spectrometry, sometimes it exceeds the quality control limit.Influences, such as current, voltage, equipment(internal circulating water, 10%CH4+90%Ar, and vacuum) checking, instrument monitoring, sample cleaning, and oper-ators, were investigated by means of 6-sigma and lean operations to improve accuracy.

Microstructure of Hot-Dip Galvanized Zn-Al-Mg Alloy Coating

The microstructure of hot-dip galvanized Zn-11%Al-3%Mg-0.2%Si alloy coating was studied in this article.X-ray diffraction analysis revealed the coating is composed by Zn,Al and MgZn2 phase.Optical microscope （OM） and scanning electron microscope（SEM） observations showed the coating is occupied by snowflake-like dendrite,double hexagonal organization and eutectic.The coating backbone was the dendrite considered to be a phase of hexagonal close-packed（HCP） structure judging form its morphology according to the crystal growth way in the coating.Transmission electron microscopy（TEM） and energy dispersive spectroscopy（EDS） researches on the dendrite suggested that an intermediate Zn-Al phase was formed at high temperature,then decomposed into a type of Zn-Al granular eutectoid after cooling down to room temperature,while the eutectoid Zn and Al had a certain crystallographic relationship.The coating solidification process and the grain crystal structure were discussed.

Lead and Cadmium Distribution in Tubes of Galvanized Steel by Hot-Dip Used for Drinking Water Supply

The main objective of this work was to evaluate the presence of lead and cadmium in galvanized steel tubes by hot-dip used exclusively for drinking water supply.In this research,samples of galvanized tubes were removed from walls of residential buildings with 30 years of use.In the process of hot galvanizing,the manufacturing standards allow or for low cost conveniences,and the use of primary zinc ingot with 1.6%metallic impurities,such as lead and cadmium,is allowed,enabling the incorporation of these metals into the zinc coating deposited on the carbon steel.The associated corrosion of these tubes can release these toxic metals,contaminating the drinking water used by residents.The samples taken from the tubes were evaluated by a square-wave anodic stripping voltammetry technique,and the results for lead and cadmium suggested randomly distributed levels,indicating that the contents of these contaminants depend mainly on the quality of the added primary zinc and the operational conditions of the immersion bath.The metallographic evaluations performed on the samples of the galvanized tubes showed irregularities in thickness and even a lack of the zinc layer deposited on the carbon steel surface.These facts suggest that galvanized tubes should not be used for drinking water.

Galvanic Skin Response—Extinction Biofeedback Training for Psychogenic Abdominal Pain: A Validation Protocol

Abdominal and pelvic pain of psychogenic origin is a widespread, disabling, difficult to identify, and often inadequately treated medical condition. This condition is often associated with poor quality of life due to high pain interference with daily activities. Cognitive behavioral psychological therapy and neuromodulation with biofeedback are validated therapies for the treatment of this condition. Aim of the present research work is the validation of a therapeutic protocol that involves the use of both techniques in combination. 20 patients diagnosed with psychogenic abdominal pain, of both sexes, aged between 18 and 60 years who had not benefited from pharmacological therapies were enrolled. 10 patients were randomly assigned to the control group (psychological treatment only), another 10 patients were assigned to the study group (neuromodulation with biofeedback-Galvanic skin response-extinction in combination with psychological therapy). For both groups, the pain score, interference of pain with daily living activities, pain relief, and the share of anxiety associated with the pain condition were evaluated (pre- and post-treatment). The patients who underwent the combined treatment achieved statistically significant better scores than patients in the control group, respectively −4.9 ± 0.9 vs −1.0 ± 0.4 for Pain;−5.1 ± 1.1 vs −0.9 ± 0.3 for Interference with life;−7.2 ± 3.7 vs −2.2 ± 2.1 for HAMA;4.6 ± 1.2 vs 1.1 ± 0.6 for Relief.

Rare earth and silane as chromate replacers for corrosion protection on galvanized steel

The present work aimed at using rare earth lanthanum salt and trimethoxy（viny）silance as chromate substitutes for galvanized steel passivation, in contrast to zinc coating samples treated with chromate.The corrosion resistance was assessed by electrochemical impedance spectroscopy（EIS） and neutral salt spray tests（NSS）.Scanning electron microscopy（SEM） was used to characterize the sample surfaces.The organic coating adhesion on the panel was also investigated via varnishes-cross cut tests.The results indicated that rare earth and silane two-step treatment gave more effective anticorrosion performance than Cr, which also provided good paint adhesion.The coating formation mechanism was also discussed.

Post treatment of silane and cerium salt as chromate replacers on galvanized steel

A complex film on hot-dip galvanized steel sheet（HDG） was prepared by immersing the sheet in 0.1wt.% Ce（NO3）3 solution and 5vol.% silane solution in turn.The corrosion protection of the complex film was evaluated by potentiodynamic linear polarization（LPR）, electrochemical impendence spectra（EIS） and natural salt spray（NSS） tests and compared with that of single cerium film and silane film.The results showed that, the presence of these films on the zinc coating hindered corrosion reaction by reducing the rate of both anodic and cathodic reaction in the corrosion process, and the corrosion protection of the complex film was much better than that of single cerium film or silane film and closed to that of chromate film, because the polarization resistance Rp and electrochemical impendence were increased markedly.Microstructure and chemical composition of these pretreated films were also investigated by scanning electron microscopy（SEM） and AES.

Cerium-tannic acid passivation treatment on galvanized steel

A novel cerium-tannic acid passivation treatment was performed on galvanized steel. The corrosion resistance of cerium-tannic passivated samples was tested by dropping test with 0.5 wt.% CuSO4 aqueous solution. The mass loss per unit area of passivated samples was measured after the corrosion in 0.5 mol/L NaCl ＋ 0.005 mol/L H2SO4 at room temperature for 96 h. The electrochemical behaviors of cerium, tannic acid, and cerium-tannic acid passivated samples on galvanized steel in 0.5 mol/L NaCl solution were investigated by polarization curves and electrochemical impendence spectra. The corrosion equivalent circuit was established according to the impedance characteristics. The results show that cerium-tannic acid treated samples exhibit better corrosion resistance than the sole cerium or tannic acid treated samples under the same condition. The mechanism of synergistic effect for cerium-tannic acid passivation on galvanized steel was discussed.