The characterization of continuous hot-dip galvanized and galvannealed steels

Dionne, S.

doi:10.1007/s11837-006-0157-y

Cited by 20 publications

(13 citation statements)

References 10 publications

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“…Therefore, galvanized coating must be free of any Fe-Zn intermetallics and ensure good adhesion to the substrate. In recent practice, galvanized bath containing low amount of aluminum (in the range of 0.2 wt%) are used to inhibit formation of Fe-Zn intermetallics by forming an extremely thin interfacial barrier layer of Fe 2 Al 5 Zn x at the substrate-coating interface [1,6]. This interfacial layer is adherent to both the matrix and the coating, without affecting the strip formability.…”

Section: Resultsmentioning

confidence: 99%

“…The use of zinc coated steels for automotive, construction and appliance applications has increased continually at a greater rate than the overall growth in steel industry during the past decade [1,2]. In hot dip galvanizing, a zinc coating is applied to the fabricated iron or steel material by immersing it in a bath consisting primarily of molten zinc.…”

Section: Introductionmentioning

confidence: 99%

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Microstructural study of galvanized coatings formed in pure as well as commercial grade zinc baths

Mandal

Das

et al. 2009

Trans Indian Inst Met

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This investigation is an effort to have a better understanding of the growth kinetics and morphology of the coating formed during the galvanizing process in pure as well as commercial grade zinc baths. The protective coating that is formed during hot dip galvanizing, normally between 450 and 480 o C, consists of a series of Fe-Zn intermetallic layers, which have been identified as gamma (Γ), delta (δ), zeta (ξ) and an outer eta (η) layer, highly rich in zinc. There is apparently no delay in the formation of ξ or δ phases in both pure as well as the commercial grade zinc baths. The gamma (Γ) phase is formed after an incubation time of about 30 s at a bath temperature of 470 o C in the pure zinc bath. Its formation is further delayed in the commercial grade zinc bath. The last morphological feature is the formation of a second ξ layer at the ξ/δ interface in the pure zinc bath. In the commercial grade zinc bath two different morphologies of ξ phase are seen starting from the lowest dipping time, and also the overall coating is considerably thicker due to formation of several iron-zinc intermetallics which degrade its ductility and outward appearance. Commercial grade zinc also enhances the dross formation in the bath and deteriorates the quality of the coating. Presence of transverse cracks as well as entrapment of dross particles in the coating is attributed to the less compact coating that is formed in the commercial grade zinc bath.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Microstructural study of galvanized coatings formed in pure as well as commercial grade zinc baths

Mandal

Das

et al. 2009

Trans Indian Inst Met

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“…A pyrometallurgical treatment for the refining of hard zinc samples was performed with the addition of different refining agents such as; zinc powder, aluminum turnings, and their mixture as shown in Figs. (1)(2)(3). Effect of addition of zinc powder on the removal of iron from hard zinc, at 650 °C for 2h, is shown in Fig.…”

Section: Characterization and Assay Methodsmentioning

confidence: 99%

“…During the process of hot-dip zinc coating, the bath becomes segregated due to cooling. This results in accumulation of crystallite of intermetallic compounds of Zn n Fe m type as precipitate which settle down as being heavier [1]. The mixed alloy of liquid zinc with intermetallic phase crystals containing 3-6 wt% Fe is called "hard zinc".…”

Section: Introductionmentioning

confidence: 99%

Removal of Iron from Hard Zinc for Production of Refined Zinc

Barakat¹

2009

TOMPJ

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Refining of hard zinc through removal of iron has been investigated in this study. Zinc powder, aluminum turnings, and mixture of both of them have been tested and evaluated as refining agents. The hard zinc samples with the additives were charged in an electric muffle furnace at a temperature range from 600 to 900°C. Iron oxide and its intermetallic compounds of Fe with Zn have been formed as a slag of refining in the sink of the crucible, while that of the intermetallic compounds of Fe with Al have been floated on the melt bath surface and skimmed. Several characterization and analytical tools, such as X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Analysis (EDAX), and Atomic Absorption Spectroscopy (AAS) were used to investigate the phases, surface microstructure, and composition of the hard and refined zinc samples. Different parameters affecting the refining process such as amount of the refining agents, refining duration and temperature have been studied. Results obtained revealed that removal of iron from hard zinc was achieved with different refining agents in the order; aluminum turnings > zinc dust> Al/Zn mixture. A refined zinc was obtained by adding 0.4 wt % Al at 700 °C after 2h of refining with lowering the iron concentration from 3.2 % in the hard zinc to 0.5% in the refined product.

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“…The presence of aluminum inhibits the formation of Fe-Zn intermetallics by forming an extremely thin interfacial barrier layer of Fe 2 Al 5 Zn x at the substrate-coating interface. [4][5][6][7] This interfacial layer (also known as a barrier or inhibition layer) is adherent to both the matrix and the coating, without affecting the strip formability. By the time the strip leaves the bath (approximately 2 to 4 seconds later), some zinc is also taken into this alloy layer, but its nature is completely different from that which occurs in absence of aluminum.…”

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confidence: 99%

Theoretical Investigation of the Interfacial Reactions during Hot-Dip Galvanizing of Steel

Mandal

Balasubramaniam

Mehrotra

2009

Metall Mater Trans A

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In the modern galvanizing line, as soon as the steel strip enters the aluminum-containing zinc bath, two reactions occur at the strip and the liquid-zinc alloy interface: (1) iron rapidly dissolves from the strip surface, raising the iron concentration in the liquid phase at the strip-liquid interface; and (2) aluminum forms a stable aluminum-iron intermetallic compound layer at the strip-coating interface due to its greater affinity toward iron. The main objective of this study is to develop a simple and realistic mathematical model for better understanding of the kinetics of galvanizing reactions at the strip and the liquid-zinc alloy interface. In the present study, a model is proposed to simulate the effect of various process parameters on iron dissolution in the bath, as well as, aluminum-rich inhibition layer formation at the substrate-coating interface. The transient-temperature profile of the immersed strip is predicted based on conductive and convective heat-transfer mechanisms. The inhibition-layer thickness at the substrate-coating interface is predicted by assuming the cooling path of the immersed strip consists of a series of isothermal holds of infinitesimal time-step. The influence of galvanizing reaction is assessed by considering nucleation and growth mechanisms at each hold time, which is used to estimate the total effect of the immersion time on the formation mechanism of the inhibition layer. The irondissolution model is developed based on well established principles of diffusion taking into consideration the area fraction covered by the intermetallic on the strip surface during formation of the inhibition layer. The model can be effectively used to monitor the dross formation in the bath by optimizing the process parameters. Theoretical predictions are compared with the findings of other researchers. Simulated results are in good agreement with the theoretical and experimental observation carried out by other investigators.

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The characterization of continuous hot-dip galvanized and galvannealed steels

Cited by 20 publications

References 10 publications

Microstructural study of galvanized coatings formed in pure as well as commercial grade zinc baths

Microstructural study of galvanized coatings formed in pure as well as commercial grade zinc baths

Removal of Iron from Hard Zinc for Production of Refined Zinc

Theoretical Investigation of the Interfacial Reactions during Hot-Dip Galvanizing of Steel

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