Electrogalvanized Research Articles

Comparative Study on the Liquid Metal Embrittlement Susceptibility of the High-Si Advanced High-Strength Steel with EG and GA Zn Coatings

The Zn-coated high-Si advanced high-strength steel (AHSS) tends to suffer Zn-assisted liquid metal embrittlement (LME) during the resistance spot welding (RSW) process. In this study, the LME behaviors of electrogalvanized (EG) and galvannealed (GA) high-Si steels were comparatively investigated. The maximum lengths of the LME cracks at the shoulder and center of the spot weld were approximately 366.6 μm and 1486.5 μm, respectively, for the EG yet 137.0 μm and 1533.3 μm, respectively, for the GA high-Si steels. Additionally, all EG and GA welded joints were etched to measure the nugget size. It was found that the increased welding current could aggravate the formation tendency of the LME cracks for both the EG and GA high-Si steels. Furthermore, the statistical results revealed that the electrogalvanized high-Si AHSS exhibited a relatively higher LME susceptibility than the galvannealed high-Si AHSS. It was deemed that the internal oxidation produced during the annealing before the Zn coating was the crucial factor that led to the difference in the LME susceptibilities for the EG and GA high-Si steels.

Uncovering the mechanism of the LME susceptibility for the galvanized and electrogalvanized DP 1180 steels

Zn-based coatings generally protect dual-phase (DP) 1180 advanced high-strength steel in automobiles from corrosion. However, liquid metal embrittlement (LME) tends to occur in Zn-coated DP 1180 steel during resistance spot welding. In this study, the LME phenomena of the galvanized (GI) and electrogalvanized (EG) DP 1180 steels were compared based on the LME susceptibility evaluation standard. For DP 1180 steel coated with GI, the maximum length of the LME crack was approximately 121.2 μm at the shoulder of the welding spot. In contrast, for the specimen coated with EG, the maximum length of the LME crack was 792.6 μm at the center of the welding spot. Owing to the different galvanizing processes, the microstructure differed during annealing, thereby influencing the occurrence of the LME. Furthermore, the microstructural observations indicated that the protection of the interfacial oxide layer in the GI specimen could prevent the formation of the LME to some extent. Therefore, the presence of the interfacial oxide layer could account for the different LME susceptibilities of the GI and EG DP 1180 steels.

A comparative study of the structure and corrosion resistance of ZnAl hydrotalcite conversion layers at different Al3+/Zn2+ ratios on electrogalvanized steel

The dissimilarities of the composition, crystal structure, and corrosion resistance of ZnAl hydrotalcite (ZnAl-HT) conversion films grown “in situ” on electrogalvanized (EG) steel substrate were investigated for different Al3+/Zn2+ ratios at pH 12. The corrosion behavior of all conversion films in 0.1 M NaCl was compared through electrochemical techniques. The composition, morphology, structure, and thickness of conversion films with different Al3+/Zn2+ ratios were characterized by Fourier-transform infrared spectroscopy (FT-IR), scanning electronic microscopy (SEM), and electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS), and X-ray diffraction (XRD). The polarization curves indicated that the ZnAl-HT films provided anodic inhibition for EG steel and the inhibition efficiency of the ZnAl-HT conversion films increases sharply with decreasing the Al3+/Zn2+ ratios from 5/1 to 5/3, while, for the 5/4 and 5/5 ratios, the corrosion resistance of ZnAl-HT conversion films showed a downward trend after two immersion hours. However, the corrosion behavior of HT conversion films with the Al3+/Zn2+ ratios from 5/3 to 5/5 remained stable for a longer immersion time. The protection performance of the ZnAl-HT films can be attributed to the barrier effects, ion-exchange competitive adsorption of chloride ions, and protective deposition of ZnO on the EG steel surface.

Enhancement of Steel Sandwich Sheet Adhesion Using Mechanical Interlocking Structures Formed by Electrochemical Etching.

Steel sandwich sheets (steel-polymer-steel), which are composed of lightweight polymers bonded on both sides with rigid steel sheets, have recently been developed as functional lightweight materials. In this study, a steel sandwich sheet (electrogalvanized (EG) steel sheet-polypropylene (PP)-EG steel sheet) with improved normal adhesion is fabricated without adhesives. Instead, adhesion is achieved via mechanical interlocking between the etched EG steel sheets and PP. Hierarchical structures were formed on the EG steel sheet surface by electrochemical etching to attain effective mechanical interlocking for improving normal adhesion without any adhesives. In the case of the EG steel sheet etched at 6 V for 7 s, a high fraction (∼35%) of holes (size: <1 μm2) with nanoscale scalloped structures was formed on the EG steel sheet surface. The normal adhesion test result of the fabricated steel sandwich sheet showed that the adhesion strength increased from virtually 0 (bare) to 559.6 kPa as a result of mechanical interlocking. The results of the focused ion beam-scanning electron microscopy and energy-dispersive spectrometry analyses confirmed the cohesive failure of PP resulting from the successful mechanical interlocking of PP with the holes formed on the etched EG steel sheet. To examine the effect of hierarchical structures on the normal adhesion of the steel sandwich sheet, finite element analysis was implemented.

Dynamic strength of laser brazed joints

Laser brazing of zinc coated steel is a well-established joining technology in the automotive industry. So far, only a few studies examined the influence of the processing parameters on the strength of these joints. Thus, the influence of different laser power adjustments on the joints’ properties is investigated. The joints are examined by the visual surface inspection, the analysis of micro-sections, quasi static tensile strength tests and dynamic bending tests. Additionally, the influence of the type of zinc coating is investigated for electrogalvanized (EG) and zinc-aluminum-magnesium (ZM) coated steel. At comparatively high laser power adjustments joints manufactured with EG coatings excel the performance of those made with ZM as joints with EG endure up to 94 % more load cycles than joints with ZM during dynamic tests.

Novel method for dynamic strength testing of laser brazed joints

Laser brazed parts made of zinc-aluminum-magnesium (ZM) coated steel show a reduced mechanical performance compared to parts made of electrogalvanized (EG) steel. However, no outstanding difference of the strength was observed in quasi-static tensile shear tests. In order to characterize the dynamic strength, relevant for laser brazed hatchbacks in automotive industry, a novel testing method was developed. At the same load, EG samples resisted seven times more load cycles than those coated with ZM. This result illustrates the necessity of the novel testing method. Furthermore, the method enables a deeper understanding about the origin of the joints’ deviant properties.

Corrosion Performance of Conversion Treatments for Electrogalvanised Steel Sheet

Fil: Di Sarli, Alejandro Ramon. Provincia de Buenos Aires. Gobernacion. Comision de Investigaciones Cientificas. Centro de Investigaciones en Tecnologia de Pinturas. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata. Centro de Investigaciones en Tecnologia de Pinturas; Argentina

Electrochemical Monitoring of Degradation Process of Galvanized Steels in Atmospheric Environments

Galvanized steels have been extensively used in auto industry, construction and household appliances etc. due to their excellent performance in corrosive atmospheric environments. Substantially, the degradation of galvanized steels could be divided into four stages: τ1 : dissolution of zinc, τ2 : sacrificial corrosion of zinc by coupling with steel, τ3 : corrosion protection by zinc corrosion products, and eventually τ4 : general corrosion of underlying steel. Lots of works have investigated the corrosion behavior of this type of material. However, there are very few works on the corrosion protection mechanism after zinc coating exhausted. Therefore, the present work focused on the corrosion stage τ3 during which the underlying steel is merely covered and protected by zinc corrosion products. It is essential to evaluate such a stage to predict the service life of galvanized steels more precisely. Based on lab experiments, the applicability of the electrochemical measurements as non-destructive evaluation methods was investigated as well. In this study, commercial electro-galvanized (EG) steel and hot-dip galvanized steel (GI) were used. For EG, the thickness of zinc coating was 3 μm, 5 μm and 10 μm, and was about 10 μm in average for GI. The samples, which were deposited with 5 g/m2 and 2 g/m2 NaCl namely, were exposed to the dry-wet cycling of 95% RH-2 hour and 40% RH-2 hour in a chamber. The corrosion process was monitored by measuring the corrosion potential and electrochemical impedance spectroscopy at some interval, and the remained amount of zinc was quantified by the anodic stripping method. In addition, the cross-section was observed by SEM, and the composition was analyzed to identify the corrosion products. Taking the results of 3 μm EG as an example, basically the corrosion potential did not rise directly right after the zinc coating disappeared. Characteristic impedance value also indicated a stage with good corrosion resistance after the zinc coating exhausted. The high frequency impedance values (ZH), which represented the sum of corrosion products and solution resistance, nearly kept stable during this period of time. Meanwhile, the reciprocal of low frequency impedance values (1/ZL) represented the low corrosion rate, which confirmed the protectiveness of zinc corrosion products. The zinc corrosion products strongly suppressed mass transports of oxygen and dissolved ferric ions. And such mechanism was proved by the cross-sectional view of the samples at τ3 stage, showing that a compact layer of simonkolleite attached to the steel surface. Finally, 1/ZL increased gradually due to the onset of the substrate steel corrosion (τ4 ), when the adhesive zinc corrosion products disappeared. As further discussion, some rust points were observed on the sample in τ3 stage during the 5 g/m2 high concentration lab test. It was supposed that the distribution of zinc corrosion product was uneven, particularly for thin zinc coating. In contrast, less rust point was observed on the samples with thicker zinc coating during the τ3 stage, and the protective effect of zinc corrosion products lasted much longer. Besides, the GI showed better performance than EG, which might be due to the crystal structure of zinc and the presence of alloy layer. Additionally, with less amount of deposited salt during the chamber test, such lab test procedure could simulate the sluggish corrosion behavior in real atmospheric environment. To conclude, by applying the non-destructive electrochemical impedance spectroscopy, the degradation stages of zinc are well distinguished. Especially the presence of τ3 stage was identified, where the underling steel was well protected by zinc corrosion products.

Development of oil canning index model for sheet metal forming products with large curvature

Oil canning is predominantly caused by unequal stretches and heterogeneous stress distributions in steel sheets, which affects the appearance of components and develop noise and vibration problems. This paper proposes the formulation of an Oil canning index (OCI) model that can predict the occurrence of oil canning in the sheet metal. To investigate the influence of material properties, we used electro-galvanized (EGI) and galvanized (GI) steel sheets with different thicknesses and processing conditions. Furthermore, this paper presents an appropriate experimental and numerical procedure for determining the sheet stiffness and indentation properties to evaluate the oil canning results. Experiments were carried out by varying the tensile force over different materials, thicknesses, and bead force. Comparison of the discrete results obtained from these experiments confirmed that the product shape characteristics, such as curvature, have a significant influence on the oil canning occurrence. Based on the results, we propose the new OCI model, which can effectively predict the oil canning occurrence owing to the shape curvature. Verification of the accuracy and usability of our model has been carried out by simulating the experiments that were done with the sheet metal. The authors observed a good agreement between the experimental and numerical results from the model. This research work can be considered as a very effective method for eliminating appearance defects from the automobile products.

Corrosion performance of Zn–Mg–Al coated steel in accelerated corrosion tests used in the automotive industry and field exposures

AbstractThe corrosion performance of Zn–Mg(1–2%)–Al(1–2%) (ZMA) coatings has been compared to zinc–iron alloy (galvannealed, GA) and zinc–aluminum coating (Zn–5Al, Galfan) as well as to conventional zinc coatings produced by hot‐dip galvanization (HDG) and electrogalvanization (EG). For this purpose, cosmetic samples (painted and uncoated) and hem‐flange panels were produced. Their corrosion performance was compared in three different accelerated corrosion tests, as regularly used by the automotive industry, e.g., VDA621‐415, N‐VDA (VDA233‐102), and Volvo STD 423‐0014. As can be concluded from our results, the behavior of ZMA coatings was strongly dependent on the testing conditions as well as on the configuration of the samples. The advantageous effect of ZMA coating was more pronounced in open situations than in confined ones, irrespective of the testing conditions. ZMA coatings provided a significant improvement in comparison to conventional coatings in tests involving a significant salt load such as VDA621‐415 or neutral salt spray especially on cosmetic configurations. By contrast, the beneficial effect of ZMA coatings was less obvious in tests with lower salt load (VDA233‐102, Volvo STD423‐0014), particularly when considering cosmetic corrosion on painted samples and corrosion in confinement. Interestingly, no significant differences were observed between samples with varying Al and Mg content in the metallic coating (1–2% each). The results were compared to data from field exposure at stationary sites.

Experimental study of initial strengths and hygrothermal degradation of adhesive joints between thin aluminum and steel substrates

Growing usage of lightweight materials such as Al and Mg alloys and composites in automotive body manufacturing has come to a point that bonding of dissimilar materials is a realistic problem to address. A significant issue related to the bonding of dissimilar materials is that the differences in substrate surface conditions, substrate chemical and physical properties often lead to bond failure at strength levels far less than the bond strength established by the adhesive manufacturer for a balanced joint. This research experimentally studied several important factors influencing initial shear strengths and hygrothermal degradation of adhesively-bonded single lap shear (SLS) joints. The effects of surface treatments such as lubrication and zinc coating on the substrates were first investigated. It was observed that even a very small change in the amount of lubricant applied to an aluminum alloy affected the initial shear strength. On the other hand, varying the amount of mill oil on a galvanized steel surface had little effect. Next, the comparative study of the initial joint strength between electro-galvanized (EG) steels and hot dipped galvanized (HDG) steels revealed that the two coatings exhibited no difference in terms of the initial strength. Also, various combinations of aluminum alloys and steel substrates were studied to observe the effect of substrate materials. It revealed that the strength of a dissimilar joint constructed of a strong substrate and relatively weak substrate fell below the strength of the like-material joint made of the relatively strong substrate, and was closer to the strength of the like-material joint composed of the relatively weak substrate. Ageing tests were performed on SLS joints at various temperatures with and without humidity. The shear strength barely changed after 60-days of exposure at various temperatures with room humidity, but degraded significantly at high temperature with high humidity.

Experimental Investigations of Bend Force in Air Bending of Electrogalvanized Steel Sheets

This article deals with bend force behavior of electro-galvanized (EG) steel sheets in air bending process. A detailed experimental study was carried out on EG steel sheets of various coating thicknesses to investigate the influence of parameters such as coating thickness, orientation of the sheet, punch radius, die opening, die radius, and punch velocity on bend force behavior. From the results, it is found that zinc coating reduces the bend force and the increase in coating thickness reduces the bend force significantly. It is observed that the bend force is larger for larger punch radius, smaller die opening, and smaller die radius. It is also observed that the bend force is larger for 0° orientation than for 90° orientation. The bend force decreases with increase in punch velocity, and this influence is more prevailing in EG sheets than in plain sheets.

Experimental Study on Surface Damage in Forming of Galvanized Steel Sheets

U-channel forming tests were performed to investigate the surface damage behavior of hot-dip galvanized (GI), galvannealed (GA) and electrogalvanized (EG) steels in sheet metal forming (SMF). Experimental results indicate that the surface topographies of galvanized steels are roughening with the number of forming in sheet metal forming (SMF) and the types and mechanisms of surface damages of the three coatings are different. And tool hardness has great effects on surface damages of the GI and GA steels while the influence of tool hardness on surface damage of EG steel is negligible.

Friction Stir Lap Welding of Magnesium Alloy to Steel: A Preliminary Investigation

An initial study was made to evaluate the feasibility of joining magnesium alloy AZ31 sheet to galvanized steel sheet in a lap configuration using friction stir welding (FSW). Two different automotive sheet steels were used for comparative evaluation of the dissimilar joining potential: a 0.8 mm thick, electrogalvanized (EG) mild steel, and a 1.5 mm thick hot-dipped galvanized (HDG) high-strength, low-alloy (HSLA) steel. These steels were joined to 2.33 mm thick AZ31B magnesium sheet. A single FSW tool design was used for both dissimilar welds, and the process parameters were kept the same. The average peak load for the AZ31-1.5 mm steel weld joint in lap shear mode was found to be 6.3 ± 1.0 kN. For the AZ31-0.8 mm steel weld, joint strength was 5.1 ± 1.5 kN. Microstructural investigation indicates melting of the Zn coating present on the steel sheets, and subsequent alloying with the Mg sheet resulted in the formation of a solidified Zn-Mg alloy layer.

Technical Note:Corrosion Protection of Electrogalvanized Steel by a Cerium-Based Conversion Coating

Abstract A new conversion coating process for electrogalvanized (EG) steel based on a cerium nitrate (Ce[NO3]3) solution with some additives has been developed that reduces the total treatment time...

Evaluation of the Corrosion Resistance of Different Galvanized Steels Treated in Cerium Salt-Based Solutions

Various treatments based on cerium salts have been evaluated in an attempt to develop surface modification treatments for galvanized steels that can replace the presently used processes that are based on hexavalent chromium. The substrates used in this study included pure zinc, electroplated zinc and zinc-nickel as well as hot dipped zinc and zinc-iron. In initial screening tests Zn and hot dipped Zn were immersed in Ce(NO3)3 or CeCl3 + H2O2 solutions at different concentrations and treatment times. The films formed in these solutions were sealed in Na2SiO3. The effect of the substrate chemistry was studied for bare electroplated zinc, zinc-nickel and hot dipped zinc as well as samples treated in a Ce(NO3)3 solution. Based on these results a new conversion coating process for electrogalvanized (EG) steel based on a cerium nitrate solution with several additives such as colloidal silica and silane has been developed that reduces the total treatment time to 70 seconds. The treated EG sample passed the 72 h salt spray test without white rusting. Similar improvements of corrosion resistance were obtained for the other types of galvanized steel.

Development of environmentally friendly nonchrome conversion coating for electrogalvanized steel

The toxicity of chromium salts created environmental and health-related concerns and generated a great deal of interest in developing chrome-free conversion coatings. Most of the new developments are based on organic coatings. In the present work, some silanes were used to coat electrogalvanized (EG) steel sheets for corrosion protection. Contact angle measurement, Tafel studies, electrochemical impedance spectroscopy (EIS) and salt spray tests (SST) were conducted to investigate the efficiency of the organic coatings for the corrosion protection. It was found that pH of a silane solution is important in the adsorption of silanes on the EG steel surface and, therefore, affected its corrosion resistance.

Influence of drying temperature on the corrosion performance of chromate coatings on galvanized steel

AbstractThe influence of drying temperature on the corrosion performance of chromate coatings on electro‐galvanized (EG) steel has been investigated using electrochemical impedance spectroscopy (EIS) and potentiodynamic measurements in 3.5% NaCl solutions. The chromate coatings were applied to the EG steel in a solution (pH 1.2) containing sodium dichromate and sulfuric acid at room temperature. The coatings were dried in an oven at three different temperatures: 60, 110 and 210°C. The surface of the chromate coatings was analyzed using atomic force microscopy (AFM) and scanning electron microscopy (SEM) combined with energy‐dispersive spectrometry (EDS). The results show that the drying temperature significantly affects the morphology of the chromate coatings and consequently affects their corrosion behavior. The chromate coatings dried at 110°C had few cracks and the lowest corrosion current. The chromate coatings dried at 60°C showed passivity. The EIS results show that the chromate coatings dried at 60°C has the largest impedance in a neutral 3.5% NaCl solution. Drying at higher temperature (210°C) degrades the chromate coatings by widening the cracks and reducing soluble Cr(VI) in the chromate layer. The favorable drying temperature for the chromate coatings on the EG steel is between 60 and 110°C.

Forming characteristics and mechanical parameter sensitivity study on pre-phosphated electro-galvanized sheet steel

With the development of modern automotive manufacturing technology, and the increased demands of automotive use, coated sheet steel has been applied in the manufacturing of large-scaled auto-panels more widely. It presents many challenges in characterizing, and understanding the behavior of coated products in terms of forming. In recent years, the increasing application of galvanized steels has highlighted the urgent need for work in this area in relation to both formability, and stamping technology. The forming characteristics of pre-phosphated electro-galvanized (EG) steel are analyzed in this paper, including the effect of a zinc coating on formability, zinc damage characteristics, and relationship between the coefficient of friction, and the viscosity of lubricants. In addition, the sensitivity of the material mechanical parameters of sheet steel to the stamping process of an auto-panel is discussed. It is shown that compared with other zinc-coated steel the application of pre-phosphated film to electro-galvanized steel prior to its being subjected to stamping operations will increase the formability, and reduce the coefficient of surface friction. With the increase of the viscosity of lubricants, the coefficient of friction of both pre-phosphated EG, and EG sheet steel decrease. Electro-zinc coatings have little influence on the mechanical properties, and the forming limit of sheet steel, but they will affect the strain distribution in the stamping process. Because of their relatively low hardness, the coatings of electro-galvanized, and pre-phosphated electro-galvanized steel are much easier to deform with the substrate than galvannealed steel, so that cracks occur later, and are to a lesser extent. It can be seen that the mechanical parameters, σs/σb, N value, R value, and δ, are relatively sensitive to the forming process under the bulging-deep drawing deformation of pre-phosphated electro-galvanized sheet steel.

Forming characteristics and mechanical parameter sensitivity study on pre-phosphated electro-galvanized sheet steel

With the development of modern automotive manufacturing technology, and the increased demands of automotive use, coated sheet steel has been applied in the manufacturing of large-scaled auto-panels more widely. It presents many challenges in characterizing, and understanding the behavior of coated products in terms of forming. In recent years, the increasing application of galvanized steels has highlighted the urgent need for work in this area in relation to both formability, and stamping technology. The forming characteristics of pre-phosphated electro-galvanized (EG) steel are analyzed in this paper, including the effect of a zinc coating on formability, zinc damage characteristics, and relationship between the coefficient of friction, and the viscosity of lubricants. In addition, the sensitivity of the material mechanical parameters of sheet steel to the stamping process of an auto-panel is discussed. It is shown that compared with other zinc-coated steel the application of pre-phosphated film to electro-galvanized steel prior to its being subjected to stamping operations will increase the formability, and reduce the coefficient of surface friction. With the increase of the viscosity of lubricants, the coefficient of friction of both pre-phosphated EG, and EG sheet steel decrease. Electro-zinc coatings have little influence on the mechanical properties, and the forming limit of sheet steel, but they will affect the strain distribution in the stamping process. Because of their relatively low hardness, the coatings of electro-galvanized, and pre-phosphated electro-galvanized steel are much easier to deform with the substrate than galvannealed steel, so that cracks occur later, and are to a lesser extent. It can be seen that the mechanical parameters, σs/σb, N value, R value, and δ, are relatively sensitive to the forming process under the bulging-deep drawing deformation of pre-phosphated electro-galvanized sheet steel.