Zinc Coated Steel Sheets Research Articles

Microstructural Investigation and Mechanical Properties of Resistance Spot Welding Joints of Mild Steel Sheets

Due to its high productivity, low cost, and increased work efficiency, resistance spot welding (RSW) can instantly join two or more steel sheets and it is widely used in the automotive industry and lately in the manufacturing of thin-walled cold-formed steel constructions. However, the RSW of zinc-coated mild steel sheets presents metallurgical challenges, especially when different thickness combinations are used. Therefore, in the present paper a resistance welding machine was used which uses direct current (MFDC) inverter technology combined with SMART AUTOSET technology to weld S250 GD and S350 GD galvanised mild steel sheets with different thicknesses. It is well known that, due to the elevated temperature that occurs during the welding process, followed by rapid cooling, defects such as cracking, porosity, lack of fusion, and an increased amount of brittle phases affect the welding quality. Therefore, the influence of the RSW process parameters established by an automatic sequence on the nugget geometry, microstructure, and mechanical properties was investigated. The phase transformations that took place during the heating-cooling cycle were analysed in detail through metallographic studies. The results showed that the microstructure of the weld nuggets was similar, characterised by columnar grains elongated in the direction of heat evacuation. Nevertheless, there were differences in terms of phase dispersion, defects and mechanical properties that have been linked to the RSW process parameters.

Experiment and design of cold-formed steel equal-leg lipped angle under axial compression

To study the buckling behavior and the design method of the load-carrying capacity of cold-formed thin-walled lipped angle, axial compression tests were carried out on 32 lipped angle columns with different sections and slenderness ratios which were manufactured with high strength zinc-coated grades G450 structural steel sheets. The experimental results showed that the long column with a small width-to-thickness ratio displayed global flexural-torsional buckling, local buckling was found for the short column with a large width-to-thickness ratio. Other specimens demonstrated interactive buckling with local buckling and flexural-torsional buckling. The specimens with torsional buckling all showed post-torsional buckling strength. Then ABAQUS finite element software was used to simulate the lipped angle specimens. The simulation results were in good agreement with the test results about buckling modes and ultimate strength which indicated that the established finite element analysis model was reasonable and feasible. Therefore, the influences of the slenderness ratio, width-thickness ratio, and width ratio of the leg to lip on the ultimate strength of cold-formed thin-walled lipped angle were analyzed using finite element software. The analysis showed that the ultimate capacity of the angle decreased greatly with the increase of the slenderness ratio. The ultimate capacity increased in the range of width-to-thickness ratios of 15–30 when the angles had the same lengths. The increasing of the width of the lips increased the ultimate capacity, but the increase of the ultimate capacity of the angles would lower when local buckling occurred at the lips. Finally, based on the test results, the modified effective width method and direct strength method were proposed to calculate the capacity of the cold-formed thin-walled lipped angle under axial compression. The comparison between the predicted results with the test and finite element analysis showed that the proposed methods were accurate and feasible.

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.

Insight into keyhole and melt pool dynamics in laser welding of zinc-coated steels by means of high-speed synchrotron X-ray imaging

Laser welding zinc-coated steels is of major importance in automotive engineering and other industries to ensure cost-effective corrosion resistance of assemblies without requiring post-weld rework. However, the low evaporation temperature of zinc is causing welding defects, in particular melt ejections and spatter. In this work, in-situ experiments of laser beam welding were performed using high-speed synchrotron X-ray imaging (up to 40,000 images/second) to determine the dynamics in the keyhole and in the weld pool and to provide detailed explanations for the formation of weld defects. A simplified sample geometry made it possible to weld zinc-coated steel sheets (DX51D Z275) in a lap joint (sheet thickness 1.25 mm each) with a fiber laser (COHERENT HighLight FL-ARM 8000) to describe fundamental phenomena. The high spatial and temporal resolution of the radiography allowed describing the acting mechanisms and their effect on keyhole and melt pool.

Simulation of Corrosion Phenomena in Automotive Components: A Case Study.

Mathematical modelling and software simulation nowadays are very effective tools for both understanding and predicting corrosion processes and the protection of metallic components. COMSOL Multiphysics 5.6 software provides validated mathematical models that can be used, for a given geometry, as a tool to predict and prevent corrosion of components. The corrosion of zinc-coated steel sheets has been studied in this work by comparing results of the simulations with laboratory tests carried out in a salt spray. Results of both the mathematical modelling and empirical tests give the possibility to estimate the stability of the protective zinc layer over time. The examination of the discrepancies between two analytical methods for the investigation of corrosion phenomena leads to possible modifications in the model in order to reach as much as possible coherence with experimental data. As a final result, a computational model of corrosion phenomena in an automotive component has been reached, allowing in the future to partially substitute laboratory tests, usually being highly time consuming and expensive.

Web crippling tests on cold-formed high strength steel channel sections having different stiffened flanges and stiffened web

This paper reports 59 tests on cold-formed high strength steel channel sections with different stiffened flanges and stiffened web. The test specimens were brake-pressed from high strength zinc-coated grades G450, G500 and G550 structural steel sheets. The test program consisted of 6 series of channel sections having different stiffened flanges, web slenderness, material strengths and loading conditions. The loading conditions were End-Two-Flange (ETF), and Interior-Two-Flange (ITF) loadings as specified in the North American Specification for cold-formed steel structures. The web crippling test strengths and load–displacement relationships of the channel section specimens were obtained from the tests. The channel sections having stiffened flanges as well as the channel sections having stiffened web enhanced the web crippling strengths of the specimens, especially for those specimens loaded under ETF loading condition. The web crippling test strengths were also compared with the design strengths calculated using the current North American Specification and European Code for cold-formed steel structures. In addition, reliability analysis was performed to assess the reliability of the design rules. Generally, it is found that the predictions obtained from the North American Specification are unconservative and unreliable for the cold-formed high strength steel channel section specimens, except for the specimens with unstiffened flanges under ITF loading condition, while the European Code was unreliable but conservative in predicting the web crippling strengths, except for the specimens with unstiffened flanges under ETF loading condition.

Experimental investigation on cold-formed steel Z-sections having different stiffened flanges undergoing web crippling

This paper presents the results of an experimental investigation comprising 55 tests on cold-formed high strength steel Z-sections having different stiffened flanges undergoing web crippling. The test specimens were brake-pressed from high strength zinc-coated grades G450, G500 and G550 structural steel sheets. The material properties of the cold-formed steel Z-section specimens were obtained by tensile coupon tests. The experimental program consisted of 4 series of Z-sections having different stiffened flanges, web slenderness, material strengths, bearing lengths and subjected to different loading conditions. The loading conditions were End-Two-Flange (ETF), and Interior-Two-Flange (ITF) loadings as specified in the North American Specification for cold-formed steel structures. The web crippling test strengths and load–displacement relationships of the Z-section specimens were obtained from the tests. The loading condition and bearing length had a considerable effect on the web crippling test strengths. The presence of lips of the Z-sections increased the web crippling test strengths of the specimens loaded under ITF loading condition. The web crippling test strengths were compared with the design strengths calculated using the current North American Specification and European Code for cold-formed steel structures. In addition, reliability analysis was performed to assess the reliability of the design rules. Generally, it is found that the predictions obtained from the North American Specification are unconservative for most of the cold-formed high strength steel Z-section specimens, except for the specimens with unstiffened flanges loaded under ITF loading condition, while the European Code conservatively and reliably predicted the web crippling strengths for all the Z-section specimens loaded under ETF and ITF loading conditions. A modification of the constants used in the European Code design equations is proposed in order to provide more accurate and reliable web crippling design strengths.

GMA process development for pore-free zinc-coated steel sheet welding in automotive industry

GMA process development for pore-free zinc-coated steel sheet welding in automotive industry

Compound Casting of Aluminum with Sheet Steel in 3D Sand Casting Using an Inductive Heating System

Compound casting is a process in which a single component is made from two metallic materials, such as aluminum and steel. Solid-liquid bimetallic compounds can be produced by suitable process control. This technology can reduce the number of joining processes, and the specific properties of the respective metal component can be used for specifically designed product properties, for example, where lightweight and high strength are needed. This paper presents an experimental methodology for producing a purely material-bonded bimetallic joint from cast aluminum and zinc-coated sheet steel in 3D sand casting using an inductive heating system. The process-related temperature characterisation in the compound zone is described using a heating test rig and temperature measurements. It shows that inductive preheating can only produce a material bond between the aluminum casting and the coated steel sheet. Shear tensile tests showed strengths between 15 MPa and 22 MPa. Laser surface pre-treatment using laser ablation cutting on the coated steel sheet was carried out to investigate the benefit of possible microform-locking. The results show a strength-reducing influence on the tensile shear tests. Micrographs showed the formation of Al4.5FeSi and Al7Fe2Si, as well as the formation of other undefined intermetallic phases. The thickness of the compound zone is 10 µm.

The Effect of V-Bending Parameters Utilizing Electrolytic Zinc-Coated Steel Sheet (SECC) Material

This study discusses the phenomenon of spring-back and spring-go in the bending kinematic forming using V-bending dies process and Electrolytic zinc-coated steel sheet (SECC/JIS G 3313) material. The zinc layer on the galvanized steel surface should not be damaged during the material forming process. The zinc layer on the galvanized steel sheet will affect the metal forming process. This study uses an experimental design with four input parameters, namely v-die opening L (mm), punch angle (degree), punch speed (mm/minutes), and bending force (kN). The smallest spring-back was obtained in the 4th test sample: the v-die opening of 35 mm, the punch angle of 40o, the punch speed of 30 mm/minute, and the bending force of 7.50 kN. The minor spring-back degree was 1.67o. Meanwhile, the smallest spring-go obtained in the second sample, namely the v-die opening of 30 mm, the punch angle of 50o, the punch speed of 40 mm/minute, and the bending force of 7.00 kN, the minor spring-go degree of 0.92o was obtained. These results show that the best spring-back degree for SECC/JIS G 3313 material is obtained when the bending process is performed with the v-die bending parameter of 30 mm, punch angle of 50o, punch speed of 40 mm/minute, and bending force of 7.00 kN.

Effect of Welding Mode on Remote Laser Stitch Welding of Zinc-Coated Steel With Different Sheet Thickness Combinations

Abstract This paper studied the effects of two welding modes, i.e., keyhole penetration and full penetration, on laser welding of two zinc-coated steel stack-ups of the same total sheet thickness but different sheet thickness combinations. The effects of welding modes on keyhole and spatter behavior were studied. It was found that keyhole penetration welding led to little spatter and mass loss for a thick-gage stack-up of the same top and bottom sheet thickness (two 1.5 mm zinc-coated steel sheets, viz., Stack-up S). This was confirmed by numerically calculated low Zout values which indicate a low potential of spatter due to zinc outgassing insufficiency. For a stack-up of thin top and thick bottom sheet combination (1.1 mm/1.9 mm, viz., Stack-up D), full penetration mode is more preferred generating less spatter than the keyhole penetration mode. This was attributed to an enlarged keyhole size at the faying interface in the full penetration mode and the relatively thinner top sheet (1.1 mm thick) compared to the bottom sheet (1.9 mm thick). It was confirmed by the low average and maximum values of Zout. In summary, to reduce the spatter in laser welding of zinc-coated steel, the keyhole penetration mode welding is preferred for the stack-up with the top and bottom sheets of similar thickness, and the full penetration mode is more suitable for the stack-up having a much thinner top sheet than the bottom sheet.

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.

Formation of long-range ordered intermetallic η''' phase and the involvement of silicon during welding of aluminum-steel sheets

EN AW-6016-T4 aluminum alloy sheets were joined with zinc-coated DC04 steel sheets using the Cold Metal Transfer (CMT) welding process. Si-rich and virtually Si-free commercial filler alloys Al-3Si-1Mn (AA-4020) and Al-4.5Mg-Mn-Zr (AA-5087) were used. The influence of silicon on the formation and morphology of intermetallic phases in the joints was studied. The intermetallic seam was investigated by scanning electron microscopy (SEM), electron microprobe microanalyzer (EPMA) using wavelength dispersive spectroscopy (WDS), and transmission electron microscopy (TEM) using selected area electron diffraction (SAED), energy dispersive spectroscopy (EDS), and electron energy loss spectroscopy (EELS). Short-range ordered (SRO) η-Al 5 Fe 2 , long-range ordered (LRO) η'''-Al 5 Fe 2 , and θ-Al 13 Fe 4 phases formed in the Si-poor and Si-rich welds. The presence of Si in the filler metal leads to the additional formation of the α c -Al(Fe , Mn)Si phase. Grains containing η and η''' were identified. The continuous η seam was generally thinner for higher Si contents. It was found that Si contents higher than 3-3.5 at% in the η seam suppressed the formation of LRO η''' and favored the formation of η. • Impact of Si in the filler alloy on the intermetallic seam of Al-steel sheet joints. • Observation of the low-temperature stable, long-range ordered η”'-Al x Fe y phase in industrial welds. • Correlation between Si content and the formation of the η-type phase. • Domain formation of short-range and long-range ordered regions.

Optimization design of high-strength cold-formed steel stiffened lipped channel columns under axial compression

In China's current market, there are many cold-formed thin-walled members used to construct low-rise light steel buildings. The members are mainly manufactured by 550 MPa yield strength aluminized zinc-coated steel sheets with a width of 180 mm. Since the load-carrying capacity of different section shapes significantly varies within a constant sectional area, finding the section shape with the highest load-carrying efficiency is one of the key problems. In this paper, the optimal section under axial compression is investigated. Initially, a program was written to select several candidate sections with high efficiency based on the theoretical load-carrying capacity calculation. Then, finite element analyses and loading tests were carried out on the selected sections, and the section with the highest load-carrying capacity was determined as the optimal section. The results indicate that the variation trends of the load-carrying capacity of the members with different section sizes obtained by theoretical calculation, finite element simulation, and loading test were consistent. When the ratio of web height to the sum of flange and lip width is between 1 and 2, the axial load-carrying capacity of the member is relatively high. The distortional buckling capacity is relatively higher when the lip width is larger. The short columns with optimal sections undergo local-distortional interaction buckling, whereas the long columns with optimal sections undergo the interaction among local, distortional, and overall buckling. The optimal section size, i.e., web height of 81 mm, flange width of 37.5 mm, and lip width of 12 mm, is proposed for engineering design reference.

Beam-Column Tests of Cold-Formed Steel Built-Up Closed Sections

This study aimed to investigate the buckling behavior of cold-formed steel built-up closed section members subjected to combined minor axis bending and compression. The channels were fabricated from zinc-coated steel sheets of grades G500 and G550 to compose built-up closed sections. A total of 30 beam-column specimens with nominal member lengths of 300, 900, and 1,500 mm as well as nominal plate thicknesses of 0.75 and 1.2 mm were eccentrically loaded under pin-ended boundary condition. The initial loading eccentricity was varied for the specimens in each test series to obtain the data evenly distributed in the axial load-moment interaction diagram. Experimental results including failure modes, loading capacities, and full-history responses of the test specimens were obtained. In addition, the experimental loading capacities were compared with nominal strengths to evaluate the suitability of the provisions as stipulated in the North American specification, Australian/New Zealand standard, European code, and American specification for the built-up section beam-columns. It is shown that the aforementioned design codes are overall unreliable and unconservative for strength predictions of the cold-formed steel built-up closed section members under combined minor axis bending and compression.

Numerical study of the effect of workpiece thickness on the interfacial behavior of a molten aluminum droplet on a zinc-coated steel sheet

In brazing, the interfacial conditions between the molten filler material and the solid workpiece are important, yet they cannot be observed experimentally. A two-dimensional axisymmetric simulation was conducted to analyze the behavior of a single droplet of molten aluminum on zinc-coated steel sheet as a simplified brazing process. The simulation models were verified through a comparison with experimental results in terms of bead shape, zinc distribution, and molten metal behavior. The results show that Young’s equation was not valid in explaining the wetting behavior because of the instant solidification. In this respect, the effects of the workpiece thickness and wetting angle on the bead width were negligible. Two periods of time, namely, the times for the temperature difference and solidification and their ratio (interface number), were defined to analyze the temperature behavior at the interface over time as well as the effects of workpiece thickness. The interfacial temperature behaviors tended to be divided into three regions: linear (or inversely proportional), singular, and convergence. The interface number converged to a value of one with the increase in the thickness.

PERANCANGAN ULANG TATA LETAK FASILITAS PRODUKSI MENGGUNAKAN METODE ALGORITMA CRAFT PADA PT. SERMANI STEEL MAKASSAR

Factory layout is one of the most important problems in a company, because the arrangement of facilities affects the efficiency and cost of manufacturing products. PT. Sermani Steel of Makassar City is one of the companies engaged in the manufacture or production of zinc-coated steel sheets (Zn) with a production capacity of 3000 tons/year, the problem that occurs is that the layout of related departments is far apart, causing large moving costs. The CRAFT Algorithm method is an improvement program that seeks optimum planning by making improvements in stages with the help of the WinQsb software. The CRAFT algorithm method can describe each department and calculate the Material Handling Cost (OMH) experienced by the product during the production process. Based on the results of research conducted, the cost of moving materials in the initial layout is Rp. 1,636,270,800/year after repairing the layout of the facility, the transfer fee is Rp. 1,467,309,300/year with a difference of Rp. 168,961,500 per year, material transfer costs have decreased by 10% from the initial layout.

Lubricant Evaluation Technique for Single Point Incremental Forming Process

Single-point Incremental Forming (SPIF) is highly flexible dieless forming process suitable for a small batch production. The higher the feed rate and tool rotational speed, the higher the production rate will be. Therefore, the selection of the suitable lubricant is a key important factor to maintain the formability of the material when increasing the feed rate and tool rotational speed. This paper proposes the technique to evaluate and later on select the proper lubricant for these conditions. This technique was divided into two phases; 1) screening, and 2) stabilization. The screening phase is a quick method for preliminary selection of the lubricants. The stabilizing phase is a step to evaluate reliability as well as ensure efficiency of the lubricant throughout the process, because of the significant increase of the forming temperature which affects directly to the performance of the lubricant. Two types of lubricants, namely solid (Graphite) and liquid (Callington Calform NF-206) lubricants mixed with the base oil (coconut oil) at different ratios were tested. The cold rolled hot-dipped zinc-coated steel sheet with thickness of 0.176 mm. and wall angles of 45, 50, 55 and 60 degrees with the depth of each wall angle of 5 mm were used. During the screening phase, the fifteen mixtures firstly were tested by using the achieved maximum wall angles without fracture as a criterion. Later on, the lubricant mixtures which could successfully form at the wall angle of 60 degrees with the forming depth of 20 mm would be tested in the stabilization phase to evaluate the formability and the forming temperature. The results showed that during the screening phase 11 lubricants could perform successfully, while the stabilization phase with the wall angle of 60 degrees only 3 lubricants could successfully form the workpiece. Therefore, this evaluation technique could help to evaluate and, for later on, be a criterion to select the select lubricant.

Study on Real-Time Porosity Defect Detection Through Neural Network Structure Optimization using Genetic Algorithm in GMAW

Zinc-coated steel sheets are widely applied as automotive chassis parts because they have high corrosion resistance and good compatibility. However, in the gas metal arc welding (GMAW) process, serious porosity defects occur due to zinc vapor generated during welding, which causes problems such as durability or productivity reduction in the welded structure. To secure weldability and productivity, it is essential to secure monitoring technology that determines whether porosity defects are generated in real-time. To solve this problem, this study provides a method of extracting feature variables from arc voltage signals generated during welding and optimizing the hyper parameters of the porosity detection algorithm deep neural network (DNN) which be learned with feature variables by applying genetic algorithm (GA). To verify the performance of the proposed method, as a result of applying it to the optimized DNN model using the experimental data of the GMAW experiment using a high-strength zinc-coated steel sheet, a prediction accuracy of 93.1 % was derived, which is improved by 3.60 % than DNN model from previous research.

Metallurgical Analysis as a Useful Method for Fire Investigation: the Case of Galvanized Steel Sheets

In this work, fire simulations were carried out on zinc-coated steel sheets usually employed for the structural parts of furniture, transformer rooms and aeration pipes. The thermal alteration induced by the fire was simulated by heating samples at 13 different temperatures (from 20° C to 1050° C) and for different exposure times (1 h and 6 h) in a laboratory furnace. The metallurgical investigation concerned the surface coloring by photographic analysis, the morphology and chemical composition of the surface oxides by SEM and EDS and the microstructure modifications as a function of the temperature by LOM. The influence of the different parameters was discussed by a statistical approach. The obtained results allowed to associate the temperature to one or more alteration of the steel microstructure and of the color, the morphology and the chemical composition of the surface oxides.