Al-Zn Alloy Coated Steel Sheet Research Articles

Influence of Cold Rolling Process on Mini Spangle Formation of 55%Al-Zn Alloy Coating Steel Sheet

According to that mini spangle is the most common defect affecting the appearance quality of hot-dip 55%Al-Zn alloy coated steel sheet, industrial experiments and statistical analysis were done to investigate the influence of cold rolling process on the formation of mini spangle. The results show that, with the decrease of rolling oil concentration, the increase of rolling time, and the increase of rolling pass, the probability of mini-spangle formation increases. Due to the different equipment conditions, the probability of mini-spangle formation on the upper and lower surfaces of steel strip is different. The reason of mini-spangle formation lies in the presence of carboxylates (R-COO-Fe) result from the residual emulsion on the surface of cold rolled steel strip. The carboxylates may interfere with the interfacial reaction between the steel substrate and Al-Zn bath, and result in more convex Fe5Si2Al20 phases formed on the surface of intermetallic compound layer. The Fe5Si2Al20 phases may provide more heterogeneous nucleation sites for the formation of Al-rich dendrites and lead to the formation of mini spangle.

Influence of Process Conditions on Spangle Size of 55%Al-Zn Alloy Coated Steel Sheet

Statistic analyses of industrial experimental datum were done to investigate the effect of pretreatment process, hot-dip process and posttreatment process on spangle size of hot-dip 55%Al-Zn alloy coated steel sheet. The results show that, with the decrease of concentration of degreasing solution, the decrease of RTF dew point temperature, the decrease of temperature at which strip entering into Al-Zn bath, and the increase of injection pressure of air knife, spangle size decreases; with the increase of hydrogen content in RTF, spangle size decreases firstly and then tends to be stable; with the increase of bath temperature, spangle size increases firstly and then decreases; The hot-dip time, the distance between air knife and steel strip, the height of air knife from Al-Zn bath, and the blowing rate of cooling fan have little effect on spangle size; the addition of mixed rare earth doesn’t affect spangle size, while the addition of titanium with trace amount leads to the decrease of spangle size.

Characterization of a Chromium-Free Passivation Coating on Hot Dip Al-Zn Allay Coated Steel Sheets

The hot dip Al-Zn alloy coated steel sheet was passivated with chromium-free passivation solution which adopted the molybdate and acrylic resin as the main film-forming substances. The surface morphology and corrosion performance of the coating were studied experimentally by using glow discharge optical emission spectroscopy(GD-OES), scanning electron microscopy(SEM) and energy-dispersive X-ray spectroscopy(EDS), polarization curves and the neutral salt spray test. The GD-OES and SEM results show that the molybdate-containing thin organic coating is deposited on the substrate compactly and homogeneously without obvious tiny cracks. The test results of corrosion performance show that the corrosion potential and current density of the passive films decrease obviously in comparison with those of the substrate, and the corrosion resistance of the coating is comparable with that of the chromate passivation coating.

Effect of Environmental Conditions on the Corrosion near Shear Cut Edge of 55 mass% Al–Zn Alloy Coated Steel Sheets

The purpose of this study is to clarify the effect of dry and wet processes on the mechanisms of edge corrosion of hot dip 55 mass% Al–Zn alloy coated steel sheet. The corrosion tests employed were continuous salt-spray tests and cyclic corrosion tests using NaCl solution or artificial seawater. It was confirmed that the edge corrosion is suppressed during the salt-spray test using artificial seawater. Furthermore, the suppression was not prevented by dry and wet processes. In order to reveal the corrosion mechanisms, the galvanic current and the cathodic polarization curves at exposed steel were measured and the corrosion products were characterized. It is suggested that the artificial seawater forms anti-corrosive corrosion products and that suppress the cathodic reaction on the steel which is exposed on the shear cut edge. The corrosion products are not changed by dry and wet processes. The numerical analysis also revealed the influence of the dry and wet process on edge corrosion.

Self-Healing Effect by Zinc Phosphate and Calcium Silicate Included in Organic-Inorganic Composite Coating on 55%Al-Zn Coated Steel Sheet

Recently, it has become necessary to improve the corrosion resistance of zinciferous coated steel sheets, especially 55% Al-Zn alloy coated steel sheets. However, it is known that cracks are easily generated on the surface of 55% Al-Zn alloy coated steel sheet during production processes. This is due to the hardness of the metallic coating. We studied non-chromate corrosion-preventive compounds for organic-inorganic composite coatings and found that the composite coating containing both Zn3(PO4)2 and CaSiO3 had the highest corrosion resistance among all the additives tested. The corrosion mechanism was investigated by the analysis of the specimens after corrosion test using SEM, AFM, TEM and EDX. It was found that the amorphous surface layer, which was approximately 30 nm in thickness and contained Ca, Cr, P, Si, C, and O, was newly formed on the steel surface exposed after deformation of the coating. It is presumed that Ca2+ and HPO42- are formed by dissolution of the CaO component in CaSiO3 and hydrolysis of ZnO3(PO4)2, respectively, and they react each other to form an insoluble Ca-phosphoric compound, which might inhibit the corrosion of metals exposed in the cracks.

Effect of Environmental Cation Species on Corrosion near Shear Cut Edge of 55%Al–Zn Alloy Coated Steel Sheet

Hot-dip 55%Al–Zn alloy coated steel sheet has superior corrosion resistance both on flat panel and near shear cut edge in various atmospheric environments. However, the corrosion often occurs near the shear cut edge in continuous wet conditions, for example, NaCl solution spray test (SST, JIS Z2371), and this has been explained by galvanic model. In this paper, it is clarified that the corrosion near shear cut edge is suppressed by artificial sea water and its second ingredient, MgCl2.To make clear the corrosion mechanisms on MgCl2 suppression of the corrosion near shear cut edge, the measurement of cathodic polarization curve on the Fe electrode after the corrosion test using a AZ/Fe/AZ galvanic electrode, the estimation of corrosion products by numerical analysis in consideration of the substances migration and the precipitation reactions, and the analysis of corrosion products by FT-IR spectroscopy were conducted. As a result, in the galvanic condition, it is clarified that Mg(OH)2 precipitates on the Fe exposed cut edge. Moreover, the corrosion near shear cut edge is suppressed by the effect of the cathodic reaction suppression of Mg(OH)2.

55%Al-Zn 合金めっき鋼板上の有機-無機複合皮膜中に含有したリン酸亜鉛とケイ酸カルシウムによる自己修復効果

Recently, it has become necessary to improve the corrosion resistance of zinciferous coated steel sheets, especially 55% Al-Zn alloy coated steel sheets. However, it is known that cracks are easily generated on the surface of 55% Al-Zn alloy coated steel sheet during production processes. This is due to the hardness of the metallic coating. We studied non-chromate corrosion-preventive compounds for organic-inorganic composite coatings and found that the composite coating containing both Zn3(PO4)2 and CaSiO3 had the highest corrosion resistance among all the additives tested. The corrosion mechanism was investigated by the analysis of the specimens after corrosion test using SEM, AFM, TEM and EDX. It was found that the amorphous surface layer, which was approximately 30 nm in thickness and contained Ca, Cr, P, Si, C, and O, was newly formed on the steel surface exposed after deformation of the coating. It is presumed that Ca2+ and HPO42- are formed by dissolution of the CaO component in CaSiO3 and hydrolysis of ZnO3(PO4)2, respectively, and they react each other to form an insoluble Ca-phosphoric compound, which might inhibit the corrosion of metals exposed in the cracks.

Effect of Environmental Cation on Cathodic Protection of 55%Al-Zn Alloy Coated Steel Sheet

not Available.

５５％Ａｌ‐Ｚｎ合金めっき鋼板の端面腐食における環境中カチオンの影響

Hot-dip 55%Al–Zn alloy coated steel sheet has superior corrosion resistance both on flat panel and near shear cut edge in various atmospheric environments. However, the corrosion often occurs near the shear cut edge in continuous wet conditions, for example, NaCl solution spray test (SST, JIS Z2371), and it has been explained by galvanic model. In this paper, it is clarified that the corrosion near shear cut edge is suppressed by artificial sea water and its second ingredient, MgCl2.To make clear the corrosion mechanisms on MgCl2 suppression of the corrosion near shear cut edge, the measurement of cathodic polarization curve on the Fe electrode after the corrosion test using a AZ/Fe/AZ galvanic electrode, the estimation of corrosion products by numerical analysis in consideration of the substances migration and the precipitation reactions, and the analysis of corrosion products by FT-IR spectroscopy were conducted. As a result, in the galvanic condition, it is clarified that Mg(OH)2 precipitates on the Fe exposed on the cut edge. Moreover, the corrosion near shear cut edge is suppressed by the effect of the cathodic reaction suppression of Mg(OH)2.

塩水噴霧試験における55%Al-Zn合金めっき鋼板の切断端面部近傍の腐食挙動

塩水噴霧試験における55%Al-Zn合金めっき鋼板の切断端面部近傍の腐食挙動

Development of a new organic composite coating for enhancing corrosion resistance of 55% Al–Zn alloy coated steel sheet

A new organic composite coating for enhancing corrosion resistance of 55% Al–Zn alloy coated steel sheet has been developed. The new coating is composed of an insoluble chromic compound, phosphate, organic resin and specially developed corrosion-preventive additives, which effect a self-healing action in cracks generated on the surface of the steel sheet while forming. This coating is superior to usual products with inorganic chromate coating and organic resin coating in corrosion resistance of flat and formed part, good appearance and chromium insolubility.

55%Al-Zn合金めっき鋼板の皮膜特性に及ぼす化成処理皮膜成分の影響

The influence of the organic composite coating components on various properties of 55%Al-Zn alloy coated steel sheet have been investigated by salt spray test, draw bead test and the measurement of Cr fixation ratio. In addition, the relationship between these properties and the film structure was studied by SAM analysis.The coating, which was composed of newly developed Acrylic resin, phosphate and Cr compound was found to provide good corrosion resistance, formability, good appearance and film insolubility. Further, the results from the film structure analysis show that this coating was characterized by its gradient composition. The layer material in contact with the 55%Al-Zn alloy coated steel sheet is an insoluble passivation layer, rich in chromic compounds and phosphate, which provides superior corrosion resistance and film insolubility. The layer material on the outer surface consists primarily of organic resin and is sufficiently flexible to ensure good formability.This new organic composite coating on 55%Al-Zn alloy coated steel sheet is commercially produced for building materials applications.

Atmospheric Corrosion Resistance of Skyward- and Groundward-Exposed Surfaces of Zinc- and 55% Al-Zn Alloy-Coated Steel Sheet

Abstract Zinc-coated (galvanized) and 55% Al-Zn alloy-coated steel sheet was tested for atmospheric corrosion resistance for 20 years in rural (Saylorsburg, Pennsylvania), industrial (Bethlehem, Pennsylvania), moderate marine (250-m [880-ft] lot, Kure Beach, North Carolina), and severe marine (25-m [80-ft] lot, Kure Beach, North Carolina) environments. Corrosion losses were determined separately for skyward- and groundward-exposed surfaces and compared to results for conventional two-sided coupons, which gave only an average of skyward and groundward surfaces. Results were fitted to exponential equations of the form C = ATB, where C is the corrosion loss, T is time, and A and B are constants. Coating lives were estimated based upon extrapolation of these equations to the time to reach a corrosion loss equal to the coating thickness. On average, the estimated life of a skyward-exposed 55% Al-Zn alloy coating was 12 times that of a galvanized coating of equal thickness (25 μm).