Hot-dip Galvanized Steel Sheets Research Articles

Zinc fever in a painter and varnisher: a case report

BackgroundZinc fever is well described in medical literature, particularly in workers after handling zinc-containing materials at high temperatures e.g., in the welding of hot-dip galvanized steel sheets. It is not known whether zinc fever also occurs at low temperatures.Case presentationWe present the case of a 33-year-old Caucasian atopic painter and varnisher with work-related dyspnea, sweating, as well as multiple occurrences of fever. He was sent to Institute for Prevention and Occupational medicine of the German Social Accident Insurance, Institute of the Ruhr-Universität Bochum (IPA) for the evaluation of isocyanate asthma, but an inhalative challenge with hexamethylene diisocyanate was negative. Since symptoms were closely related to the use of zinc coatings at room temperature without adequate protective measures, the diagnosis of zinc fever was made. After exposure cessation the worker immediately became symptom-free. The work as painter and varnisher may be associated with various exposures to hazardous substances. Besides solvents, epoxy compounds and isocyanates, which can cause obstructive respiratory diseases; additionally, zinc-containing agents should be considered as health hazards.ConclusionsThis case demonstrates that zinc fever may occur also after application of zinc coatings by spray painting at low temperatures.

The Pre-Heating Effect for Porosity Control during the Laser Welding of Galvanized Steel Sheets

Recently, for the high performance of automobiles, the application ratio of zinc-coated steel sheets with excellent corrosion resistance has been increasing. However, it is difficult to achieve sound welds, as porosities form from zinc during welding. In this study, a laser welding process, with the addition of a pretreatment step to conventional laser welding, was devised to improve weld quality by eliminating pores caused by zinc in the welds. Laser welding was performed on the overlapping joint of hot-dip galvanized steel sheets (SGARC 340, Hyundai Steel., Suncheon-Si, Jeollanam-do, Republic of Korea), with a thickness of 1.2 mm in the upper sheet and 0.9 mm in the lower sheet, and the welding characteristics were investigated by varying the laser power and focal position. Compared to conventional laser welding, the three-step laser stitch welding process significantly reduced the degree of spatter generation and welding defects. Additionally, it increased the tensile–shear load by approximately 37%. Moreover, the reduction in the zinc component of the three-step laser stitch welds was confirmed through SEM-EDS analysis. These findings contribute valuable information for securing high-quality welding joints and effectively addressing zinc-coated steel sheet welding quality issues in the automotive and industrial sectors.

New kink-band formation mechanism discovered in Zn-Al alloy with mille-feuille microstructure

The discovery of kink-band strengthening in some Mg-alloys has focused attention on the development of mille-feuille-structured alloys composed of alternating stacks of plate-like soft and hard phases. In this study, we focused on the Zn-6.0mass%Al alloy that is composed of hcp-Zn and fcc-Al, and is used as a coating material on hot-dip galvanized steel sheet for automobile. The deformation behavior was examined by using directionally solidified crystal. As expected, kink bands formed in alloys but two different kink-band formation mechanisms were identified. One is a classical mechanism which involves the formation of an array of dislocations perpendicularly aligned with their slip planes. The other is a new mechanism which has never been reported in any materials before, and a prior {11 2¯ 2} pyramidal slip in the Zn matrix phase acts as the source, with dissociation of the <112¯3¯> dislocation supplying the <11 2¯ 0> dislocation for kink-band formation. The latter newly found mechanism introduces fine kink bands uniformly into the specimen, which effectively causes kink-band strengthening during subsequent deformation compared to kink bands introduced by conventional formation mechanism. This study provides a new strategy for enhancing kink-band strengthening in alloys by the control of the morphology of kink bands.

Diffusion Behavior of Al in Zn Coating Layer of Zn-0.2mass%Al Hot-dip Galvanized Steel Sheets with and without Temper Rolling during Aging after Production

It is known that Al added to the Zn coating layer of hot-dip galvanized steel sheets (GI) diffuses to the surface at room temperature and forms Al-based oxides in air. In order to understand the diffusion behavior of Al in Zn coating layer, this study investigated the effect of the aging temperature on the segregation behavior of Al-based oxides in GI with and without temper rolling (skinpass rolling) using a material with a Zn coating weight of about 56 g/m2 with an Al content of approximately 0.20 mass%. The specimens were aged at -15, 5, 20, 38, 100 or 200 ºC in air after production, and the surface and cross sections were observed and analyzed by XRF, SEM-EDX, EBSD and TEM. As a result, up to the aging temperature of 38 ºC, the amount of Al-based oxides increased linearly to the square root of aging time, suggesting that the formation rate is determined by the diffusion of Al in Zn coating layer in this temperature range. However, this linear relationship did not hold at aging temperatures above 100 °C. In addition, in the temper-rolled GI, the formation rate of Al-based oxides is larger than that without temper rolling up to the aging temperature of 38 ºC, and then decreased drastically at aging temperatures above 100 °C. The segregation behavior of Al-based oxides is discussed in view of the diffusion behavior of Al and the changes in the macrostructure of the Zn coating layer during the aging after production.

NUMERICAL AND EXPERIMENTAL STUDIES ON CLINCH-BONDED HYBRID JOINING OF STEEL SHEET DX53D+Z

The automotive industry is characterized by the fact that it uses an entire range of materials. These are materials with different mechanical properties, thicknesses, and even different combinations. A variety of joining methods, such as clinching, is used to join this range of materials. However, sometimes it is necessary to combine several methods of joining materials. The paper deals with the evaluation of the properties of joints, which are created by a combination of mechanical joining and adhesive bonding. Two types of adhesives were used: adhesive based on epoxy resin and adhesive based on acrylate polymers. Double-sided hot-dip galvanized steel sheets DX53D+Z with a thickness of 0.8 mm were used to join with this combination of joining techniques. Numerical simulation tools were used to assess the joinability of materials. The simulation results were verified by the results from the experiments of real test samples. Samples joined by the clinching method combined with epoxy resin adhesives achieved higher load-bearing values and no cracks or any other type of failures were observed in these joints.

Study on zinc slag defects on surface of pure hot dip galvanized steel sheet

Hot dip galvanized steel sheet is widely used in the automotive field because of its advantages of low cost, thick hot dip galvanized layer, reducing body defects, improving vehicle performance, and beautifying surface appearance. However, the zinc slag defects on the surface of the steel plate significantly reduce the surface quality of the steel plate. In this paper, the morphology of zinc slag on the surface of a pure hot-dip galvanized steel sheet was analyzed by scanning electron microscope. The results showed that the zinc slag defects on the surface of pure hot-dip galvanized steel strip was round, and the size was large, about 700 um. By adjusting the air knife pressure, the aluminum content in the zinc tank, and the opening of the RCS fan, the number and size of zinc slag defects on the surface of pure hot-dip galvanized steel strip can be significantly reduced. As a result, the steel plate was improved.

Analysis of coarse stripes of alloyed hot-dip galvanized steel sheets

Zinc iron alloy hot-dip galvanized steel sheet is widely used in the automobile and household appliance industry because of its good weldability, coating property, and corrosion resistance. In the production of alloyed hot-dip galvanized steel sheets, stripe defects are often found on the surface of the strip, which affects the diffusion reaction of iron and zinc and causes the defects to be amplified. Coarse stripes are one of the main ones. In this paper, the coarse stripe defect on the surface of an alloyed hot-dip galvanized steel plate was studied, by means of the Scanning Electron Microscope and Energy Spectrum, combined with the verification of galvanizing production. The results showed that the morphology of the coarse stripes defect area on the surface of the alloyed hot-dip galvanized sheet exhibited concave-convex features, and the average iron content was 1.41% lower, compared with the defect-free area, Indicating that the streak defect region was insufficiently alloyed. It is presumed that there is oxide in the region of the streak defect. By adopting the cleaning zone and adjusting the atmosphere in the furnace, the incidence of defects was reduced by 76%, and the quality of the slab was significantly improved.

The effect of protective and decorative coatings on the strength of adhesive joints of hot-dip galvanized steel sheets

The influence of chromate, phosphate, glossy and brightening coatings on the performance of adhesive joints of hot-dip zinc-coated steel sheets was compared. The contribution of this study has been to compare the adhesive joint strength in adherends with two types of coatings: steel sheet with zinc coating and additional coating. Two types of bisphenol A (BPA) epoxy adhesives were used to assemble the joints, that were subject to shear stresses. The surface of the adherends was described in terms of surface roughness parameters. The highest value of the shear strength was recorded for the adhesive joints of the hot-dip zinc-coated steel sheets with chromate passivation and brightening. The poorest performing joints were of the glossy galvanized steel sheets.

Development of High-lubricity Hot-dip Galvanized Steel Sheets with Excellent Press Formability for Automotive Body Panels

Development of High-lubricity Hot-dip Galvanized Steel Sheets with Excellent Press Formability for Automotive Body Panels

Diffusion Behavior of Al in Zn Coating Layer of Zn-0.2mass%Al Hot-dip Galvanized Steel Sheets with and without Temper Rolling during Aging after Production

Diffusion Behavior of Al in Zn Coating Layer of Zn-0.2mass%Al Hot-dip Galvanized Steel Sheets with and without Temper Rolling during Aging after Production

Development of Surface Modified Hot-dip Galvanized Steel Sheets “GI JAZ&lt;sup&gt;®&lt;/sup&gt;” Contributing to Excellent Design of Automotive Body

Development of Surface Modified Hot-dip Galvanized Steel Sheets “GI JAZ&lt;sup&gt;®&lt;/sup&gt;” Contributing to Excellent Design of Automotive Body

Effect of Inorganic Filler Addition on Non-Combustible and Mechanical Properties of Color Coated Steel Sheets

Recent large-scale fires in buildings and logistic warehouses have become a major social issue, involving both property loss and multiple casualties. To make color coated steel sheets non-combustible and/or have anti-fire properties, various ways of optimizing manufacturing parameters have been investigated for outer, inner, roof and ceiling panels. In the present study, the effect of inorganic filler content and size on the non-combustible and mechanical properties of color coated steel sheets has been investigated using samples prepared as pre-painted coating materials. Both salt spray corrosion and chemical resistance tests were also carried out. Filler distribution and size were measured by optical microscopy, scanning electron microscopy and glow discharge spectroscopy, and found to be critical factors affecting non-combustible performance. As the amount of added filler increased, the non-combustible property of the color coated steel sheets improved, while mechanical properties, corrosion resistance by salt spray and chemical resistances deteriorated. During 3t-bending tests, the adhesive strength at the interface between coated layer and hot dip galvanized steel sheets was rather strong, although the filler-added upper coated layer was mostly peeled off. The mechanical properties of 30% filler addition samples were compared to samples with less than 20% filler addition. The main reason for the poorer performance was clarified in terms of filler size and crack propagation in the 3t-bended color coated layer.

Root cause analysis of pinhole defects on painted galvanized steel panel

Galvanized steel sheets have been widely used in automotive industries. However, it is still a challenge for steel makers to produce defect free hot dip galvanized steel sheets especially for outer panel applications in automotive body. In this study, the root cause of uncommon pinhole defects on painted hot dip galvanized steel panel was investigated. Optical microscopy (OM), scanning electron microscope (SEM) coupled with energy dispersive spectrometry (EDS), and auger electron spectroscopy (AES) were used to characterize these pinhole defects from top surface to base steel layer by layer. A reannealing experiment was carried out to reproduce the key features of the corresponding defect on the base steel. It was found that the pinhole defects were composed of a series of connected voids in the paint layers and started from the dents on the base steel prior to hot dip galvanizing. Based on the results of coarse grains around the dents and residual boron oxides at the dent bottom, further cause of the dents was attributed to the boron containing buildups on furnace rolls in the high temperature section of hot dip galvanizing line. As the surface of furnace rolls was cleaned up, the dent defects on the base steel, the bare spot defects in the zinc coating and the pinhole defects on the painted panel were eliminated successfully.

Mechanical Behavior and Damage of Zinc Coating for Hot Dip Galvanized Steel Sheet DP600

Advanced high strength galvanized steel sheet has been one of the dominant materials of modern automotive panels because of its outstanding mechanical properties and corrosion resistance. The zinc coating thickness of hot dip galvanized steel sheet is only about 10–20 μm, which is a discarded object on the macro level. However, it is obvious to damage and impact on stamping performance. Therefore, this paper takes zinc coating as the research object and builds its mechanical constitutive model based on a nano-indentation test and dimensional analysis theory. We separated the zinc coating from the galvanized steel substrate and constructed a sandwich material model by introducing a cohesive layer to connect the zinc coating and the steel substrate. We obtained the interface binding energy between the zinc coating and the steel substrate through the nano-scratch test. The accuracy of the model is verified by the finite element analysis of hemispherical parts. We used the five-layers element model with 0 thickness cohesive layer to simulate the zinc coating damage of galvanized steel sheet. The hemispherical part drawing experiment is used to verify the feasibility of the finite element analysis results. The results demonstrate that it is more accurate to consider the finite element numerical simulation of the zinc coating, introducing the cohesive element to simulate damage between the coating and the substrate. Drawing depth, stamping force, and the strain of the numerical simulation are closer to the experimental results.

Segregation Mechanism of Al-based Oxides on Surface of Zn-0.2mass%Al Hot-dip Galvanized Steel Sheets

Segregation Mechanism of Al-based Oxides on Surface of Zn-0.2mass%Al Hot-dip Galvanized Steel Sheets

Evaluation of selected properties of coatings in respect of risk elimination of surface damage of stamped parts

Abstract For achieving a long service life of stamping dies for new types of steel sheets intended for the automotive industry, the tribosystem must be optimally designed. One of the possible solutions is its optimization by coatings. More modern coating technologies for stamping dies include PVD (physical vapor deposition) and CVD (chemical vapor deposition) methods. The properties of PVD TiCN and DLC (diamond-like carbon) coatings deposited on ledeburitic high-alloy Cr–Mo–V steel were analyzed by standard tests (coating adhesion by both the scratch and Rockwell C tests, microhardness by Vickers method and coating thickness by Calotest) and developed tribo-meter of the “friction jaw-roller” type at drawing double-sided hot-dip galvanized steel sheet. The obtained results showed better tribological behavior of the DLC coating.

Depth Elemental Imaging during Corrosion of Hot-Dip Galvanized Steel Sheet by Confocal Micro XRF Analysis.

The elucidation of the mechanism for steel corrosion under a coating layer has been attracting research attention. Herein, we utilized a confocal micro-X-ray fluorescence (XRF) analytical instrument to conduct non-destructive elemental analysis near the surface of a steel sheet. Using this method, elemental map images of steel sheet cross sections were obtained without sample destruction. To confirm corrosion suppression in the presence of Mg ions, we observed the corrosion behavior of hot-dip galvanized steel sheets immersed in an aqueous NaCl solution to which Mg ions were added. By using the confocal micro XRF system, the elution of the coating components and the precipitation process of the corrosion products were confirmed.

Press formability of newly developed high lubricity hot-dip galvanized steel sheets

Surface modification technology was applied to hot-dip galvanized steel sheets (HDG) in order to improve their press formability. The frictional behavior and press formability of surface modified HDG were investigated in comparison with those of conventional HDG, conventional electrogalvanized steel sheets (EG) and pre-phosphate treated EG (EG pre-phos). Specimens of these coated mild steel sheets with various mechanical properties were used as test materials. The friction coefficient was measured by a flat sliding test, and press formability was evaluated by a deep drawing test and a stretch forming test. As a result, surface modified HDG showed a lower friction coefficient and higher press formability than conventional HDG and conventional EG. The friction coefficient and press formability of surface modified HDG were similar to those of EG pre-phos. In deep drawing, the inflow of material from the flange area to the cracking area becomes easier due to the lower friction coefficient of surface modified HDG, which leads to improvement of deep drawability. In stretch forming, the outflows of material from the sheet/punch contact area to the cracking area become easier due to the lower friction coefficient of surface modified HDG, leading to improvement of stretch formability. These results indicate that surface modified HDG is a promising material for automotive use.

Sliding characteristics of hot-dip galvanized steel sheets depending on aging time after production

The effect of aging time after production on the frictional characteristics of hot-dip galvanized steel sheets (HDG) was examined in this study to stabilize and improve the press formability of HDG. Conventional HDG with the Zn coating weight of 67 g/m2 including 0.36 mass% Al were used as test specimens. The specimens were aged for a predetermined period, after which their friction coefficients were measured with a flat sliding test. It was found that an Al-based oxide grew on the HDG surface and the friction coefficient tended to decrease with increased aging time. This suggests that the Al-based oxide reduced the friction coefficient. To understand how the Al-based oxide affects the friction coefficient, surface observation and analysis of both the test specimens and the tools after sliding were carried out. Although the Al-based oxide was not detected on the HDG surface in the area of contact with the sliding tool, the oxide was detected as adhering material on the tool surface after sliding, suggesting that the adhering material on the tool reduced the adhesion force between the metallic Zn of the HDG and the tool. This could lead to a lower friction coefficient because shearing resistance was decreased.

Liquid Metal Embrittlement during Hot Forming of Hot-Dip Galvanized Advanced High-Strength Unalloyed Steels (AHSS)

Abstract Advanced High-Strength Steels (AHSS) are of interest as, owing to their increased strength, they are able to absorb more energy than conventional steels in a car crash. Thus, thinner metal sheets can be used for car design so that vehicle weight and fuel consumption are reduced. The elements Si, Mn, Al, and B are added in order to achieve the desired AHSS alloy properties. Corrosion protection for the automotive sheet metal is mainly ensured by hot-dip galvanizing. The sheets are further processed by hot forming. Hot-dip galvanized steel sheets made of 20MnB8 were examined after high temperature tensile tests. Metallographic examinations were performed on tensile test specimens which were tested at temperatures between 400 and 800 °C and strain rates between 0.05 and 5 s−1. Liquid metal embrittlement was observed at temperatures above 700 °C. Lower strain rates resulted in a smaller degree of liquid metal embrittlement. In order to avoid the occurrence of liquid metal embrittlement during hot forming of galvanized AHSS sheets, the relevant process parameters need to be further optimized.