Papers by Keyword: Galvanized Steel Sheet

Abstract: The present study deals with the investigation of the long term atmospheric corrosion phenomena for galvanized steel sheet in the region of Addis Ababa in Ethiopia using various atmospheric corrosion models. Addis Ababa have transforming atmosphere type of urban/industrial atmosphere, and these changes are going to affect the atmospheric corrosion phenomena for galvanized steel sheet used in this region, which is investigated through atmospheric corrosion models using atmospheric data collected from National Meteorology Agency, Ethiopia for 21 years from 2000 to 2020. Atmospheric corrosivity category for Addis Ababa is determined, and it is found that with little deviation in atmospheric pollutant these categories can shift between C2 and C3 corrosivity category for galvanized steel sheet atmospheric corrosion. Further to study the atmospheric corrosion of galvanized steel sheet, standard atmospheric corrosion models were employed namely Feliu et al. model and Kucera et al. model. These studies corroborate the findings of atmospheric corrosion of galvanized steel sheet and cross verified with the similar region atmospheric corrosion experimental studies performed earlier on the same material. All the atmospheric corrosion models confirmed the trend of the atmospheric corrosion of galvanized steel sheet in the region of urban/industrial atmosphere type. And based on the comparative analysis of all models predictions with experimental results in literature, it is confirmed that the atmospheric corrosion model results are reliable for the study of short and long period of atmospheric corrosion of galvanized steel sheet in Addis Ababa region.

Abstract: An urgent need has been identified, associated with the validity of improving the process for the manufacturing of galvanized steel, in the analysis and improvement of each stage of production in the conditions of the particular cold-rolled shop of the Iron and Steel Work. As a novelty, the processes and equipment for cleaning a hot-rolled strip, pickling a strip, rolling of pickled strips, physicochemical surface treatment, zinc coating, passivation, and other elements were reviewed from the point of view of possible corrosion consequences of the production. For the first time in the considered production system, elements and operations, their errors and imperfections, which can lead to poor-quality coating, violation of the zinc layer and reasons that contribute to the corrosion of galvanized metal products in the future, were identified at each stage.

Abstract: In the metal inert gas (MIG) weld-brazing process, the lap-joint welds between 5052 aluminum alloy and automotive galvanized steel sheet were achieved employing an automatic MIG welding machine. The different percentage of helium (He) gas addition to pure argon (Ar) shielding gas was selected to investigate the performance of lap-joint welds such as appearance of weld bead surface, weld bead geometry, microstructure, tensile strength, fracture surface of welds and thickness of intermetallic compounds (IMCs) layer between the dissimilar materials in the brazing zone. The results showed that the lap-joint welds produced by adding 5% and 10% He gas to Ar shielding gas were provided with better performance of specimens. The average tensile strength of lap-joint welds between 5052 aluminum alloy and automotive galvanized steel sheet is 206.23 MPa. In additions, the amount of porosity in the fusion zone that specimens produced by using 10% He addition to Ar-based shielding gas is less than others. It can be found that the thickness of IMCs layer between the weld bead and automotive galvanized steel sheet from 3.30 μm to 4.90 μm.

Abstract: Z11A3M, Z6A3M, Z1.6A1.6M, and Z1A1M coating samples were prepared in HDPS by traditional continuous hot dipping method. The anti-corrosion ability of these coatings was determined by SST, polarization curve and electrochemical impedance. The corrosion products were analyzed by XRD. The surface and section microstructures were observed by SEM. The results showed, the corrosion resistance of 4 kinds of Zn-Al-Mg coated steel is 4 times as galvanized steel. The Zn-Al-Mg coated steel sheets can be self-cured. MgZn₂ and eutectic could be found in all ZAM coating. Zn/Al/Zn₂Mg eutectic can be found in all 4 kind of coatings. The reason for superior corrosion resistance of Zn-Al-Mg coated steel is the decomposition reaction of Zn₅(OH)₈Cl₂ which is retained by Mg. Thus the O₂ diffusing rate is lowered down. Mg acts as PH buffer and the Zn dissolving rate can be reduced. According the results, the application of Zn-Al-Mg coated steel sheets is forecasted.

Abstract: Z11A3M, Z6A3M, Z1.6A1.6M, Z1A1M and Z1M coating samples were prepared in HDPS by traditional continuous hot dipping method. The microstructure, element distribution and phase was analyzed by SEM, EPMA and XRD. The corrosion resistance was checked in SST. The result was, MgZn₂ and eutectic could be found in all ZAM coating. The ZAM coatings showed excellent corrosion resistance in SST than GI. The corrosion resistance was 4.1 to 11 times of GI. There was no strong relativity between alloy composition and corrosion resistance due to Mg enrichment on the surface of coating. Edge-unsealed ZAM samples showed good corrosion resistance than edge-sealed sample.

Abstract: Uniaxial tension tests for galvanized steel sheets are performed. Fractured surfaces of the specimens are observed by means of the scanning electron microscope (SEM). It is confirmed that the specimens experience ductile fracture. Based on the Gurson meso-damage theory, Hill’48-GTN anisotropic damage model is presented, and used to analyze the uniaxial tension test. The true stress-strain curves are fitted by three kinds of main flow stress models. After comparing the fitting precisions, the Voce model is selected as the flow stress model for the simulation analysis. The simulation results show that the Hill’48-GTN model can be used to accurately predict the whole process of damage occurrence, evolution and fracture in tension, and void volume fraction can be taken as a forming limit parameter of sheet metal forming.

Abstract: Dark green passivation film was prepared by dipping galvanized steel in a solution made of four types of acid(chromic anhydride, phosphoric acid, nitric acid and sulfuric acid) with a certain amount of stabilizer and toner. Scanning Electron Microscopy was used to observe the morphology of the film. Elements of passivation film were conformed by using EDS. SEM showed that the surface of the film was even. Cr, O, P, S, N, Zn and a small amount of Fe were found in the film by the test of EDS.

Abstract: Modeling of resistance spot welding process on galvanized steel sheet was investigated. Mathematical models developed by nonlinear multiple regression analysis and artificial neural network approach were employed in the prediction of welding quality factors, namely nugget diameter, penetration rate and tensile shear strength, under some welding conditions. According to the prediction models on quality, the prediction systems of welding process parameters were formulated respectively on the basis of Newton-Raphson iterative algorithm and cascade forward back propagation algorithm in order to obtain the desired welding quality. The results showed that the prediction precision of cascade forward back propagation algorithm was higher than Newton-Raphson iterative algorithm. The current duration had the largest prediction error, followed by electrode force and welding current. Therefore, it was concluded that the current duration was the most difficult parameter in prediction system of welding process in order to obtain the desired welding quality.

Abstract: In order to develop an environmental friendly passive films on galvanized steel sheet, a chromium-free passive solution based on waterborne polyurethane (WPU) and Manganate was studied. The results show that the optimized compositions in passive solution are KMnO4 6g/L, (NH2)2CS 5g/L and WPU 150g/L. The passive films were prepared by dipping steel substrates into the passive solution for 10 seconds and drying at 120 °C for 30 seconds. SEM observation shows that the film’s thickness is about 1.5 µm. XRD patterns indicates that the chromate-free passive films mainly consisted of MnO2 and K2MnO4. Anticorrosion tests indicate that the chromate-free passive films can provide an excellent barrier to corrosive agents.

Abstract: The resistance spot welding process of galvanized steel sheet used in the body manufacturing of family car was studied, and the indexes of nugget geometry and tensile-shear strength of spot welds were tested. Four process parameters, namely welding current, electrode force, welding current duration and preheat current, and interactions among them were regarded as factors impacting indexes. Method using in mathematical models developing was nonlinear multiple orthogonal regression assembling design, which was optimized by the technology of variance analysis. The experimental results showed that more accurate prediction on nugget size and mechanical properties of spot welds can be obtained by the models optimized. With these prediction results, the optimization of welding process also was realized by the analysis to effect of the parameters and interactions on the welding quality.