• Journal of Welding and Joining
• /
• v.18 no.3
• /
• pp.51-59
• /
• 2000

Sink roll has been used in molten 55%Al-Zn alloy bath of continuous galvanizing line for sinking and stabilizing working steel strip in molten metal bath. In the process, the sink roll body inevitably build up dross compounds and pitting on the sink roll surface during 55%Al-Zn alloy coated strip production, and the life time of the sink roll is shorten by build up dross compounds and pitting. The present study examined the application of thermally sprayed ceramic coatings method on sink roll body for improving erosion resistance at molten 55% Al-Zn pool. In this experiment, the stainless steels such as STS 316L and STS 430F were used as the substrate materials. The CoNiCr and WE-Co powder were selected as bond coating materials. Moreover $Al_2O_3-ZrO_2-SiO_2 and ZrO_2-SiO_2$ powders selected as the top coating materials. Appearances of the specimens before and after dipping to molten 55%Al-Zn pool were compared and analyzed. As a result of this study, STS430F of substrate, WC-Co of bond spray coatings, $ZrO_2-SiO_2$ power of top spray coatings is the best quality in erosion resistance test at molten 55%Al-Zn pool

• Corrosion Science and Technology
• /
• v.23 no.4
• /
• pp.296-301
• /
• 2024

Steels have excellent mechanical properties and weldability. They are also economically producible. Thus, they are widely applied in various industries. However, they have a disadvantage in that rust can occur after a certain period of time. To compensate for this, Zn, which has excellent sacrificial corrosion resistance, can be coated on steels. With global zinc consumption increasing at the current rate, depletion is expected in the near future. Recently, POSCO has developed innovative Al-Zn-Si alloy coated steel sheets with better corrosion resistance than Zn coating. In this study, corrosion resistance, weldability, friction characteristics, and so on were evaluated compared to GI steel sheets to evaluate their applicability to automotive steel sheets. It showed excellent corrosion resistance even at a lower coating weight compared to GI steel sheet. It was also excellent in terms of galling and welding LME. Its spot welding life, electrodeposition coating, and bendability were equally excellent. This is presumed to be related to the formation of the Al-Zn-Si alloy phase at the interface of the coating layer.

• Corrosion Science and Technology
• /
• v.9 no.6
• /
• pp.233-238
• /
• 2010

Hot-dipped Al-Mg-Si coatings to alternate Zn and Zn alloy coatings for steel were examined on metallographic structure, corrosion resistance, sacrificial ability, formation and growth of inter-metallic compounds, and mechanical properties. Near the eutectic composition of quasi-binary system of Al-$Mg_2Si$, very fine eutectic structure of ${\alpha}$-Al and $Mg_2Si$ was obtained and it showed excellent corrosion resistivity and sacrificial ability for a steel in sodium chloride solutions. Formation and growth of Al-Fe inter-metallic compounds at the interface of substrate steel and coated layer was suppressed by addition of Si. The inter-metallic compounds layer was usually brittle, however, the coating layer did not peel off as long as the thickness of the inter-metallic compounds layer was small enough. During sacrificial protection of a steel, amount of hydrogen into the steel was more than ten times smaller than that of Zn coated steel, suggesting to prevent hydrogen embrittlement. Al-Mg-Si coating is expected to apply for several kinds of high strength steels.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.21 no.6
• /
• pp.64-69
• /
• 1984

We found that the maximum efficiency of Al-MIS (p-Si) solar ceil was shown at 80$\AA$ thickness of Al-film which was deposited with slower velocity than 0.6$\AA$/sec. It was coated with ZnS and SiO for Anti-Reflecting. In single coating, ZnS and SiO film had maximum Isc at 570 and 690 A thickness, respectively. We confirmed that these results agreed well with the quarter coating condition; n1d1=λ/4. In double coating, we held the one layer with its optimum thickness in single coating and controlled the other layer. The maximum value of Isc in this case was almost the same with it in single coating but was maintained its value in so wide range of thickness. Keeping the relation; n1d1=n2d2 as another way, we made the total thickness of film thinner to 70-90% of the sum of each optimum thickness in single coating. In this case Isc was higher value than 20% of it in any other previous case and was retained so wide range of thickness.

• Journal of Welding and Joining
• /
• v.19 no.5
• /
• pp.512-519
• /
• 2001

Sink roll has been used in molten Zn-0.2%Al alloy bath of continuous galvanizing line in sinking and stabilizing process of the steel strip in molten metal bath. In this process, although the scraper scraps off the sink roll surface, the dross compounds is builded up on the sink roll surface and the life time of the sink roll is shorten by the dross compounds. The present study was investigated the application of the spray coating layer on sink roll body for improving durability In molten Zn-0.2%Al alloy. Through the durability tests in molten Zn-0.2%Al alloy with various ceramic and cermet coating layer, the optimum bond and top coating material was obtained. As the results, the system of STS430F base metal, WC-l7Co bond and $ZrO_2-SiO_2$ top coating was clarified to be the best quality of durability in molten Zn-0.2%Al alloy.

• Corrosion Science and Technology
• /
• v.11 no.1
• /
• pp.1-8
• /
• 2012

The development of martensitic grades which can be processed in continuous galvanizing lines requires the reduction of the oxides formed on the steel during the hot dip process. This reduction mechanism was investigated in detail by means of High Resolution Transmission Electron Microscopy (HR-TEM) of cross-sectional samples. Annealing of a martensitic steel in a 10% $H_2+N_2$ atmosphere with the dew point of $-35^{\circ}C$ resulted in the formation of a thin $_{C-X}MnO.SiO_{2}$ (x>1) oxide film and amorphous $_{a-X}MnO.SiO_{2}$ oxide particles on the surface. During the hot dip galvanizing in Zn-0.13%Al, the thin $_{C-X}MnO.SiO_{2}$ (x>1) oxide film was reduced by the Al. The $_{a-X}MnO.SiO_{2}$ (x<0.9) and $a-SiO_{2}$ oxides however remained embedded in the Zn coating close to the steel/coating interface. No $Fe_{2}Al_{5-X}Zn_{X}$ inhibition layer formation was observed. During hot dip galvanizing in Zn-0.20%Al, the $_{C-X}MnO.SiO_{2}$ (x>1) oxide film was also reduced and the amorphous $_{a-X}MnO.SiO_{2}$ and $a-SiO_{2}$ particles were embedded in the $Fe_{2}Al_{5-X}Zn_{X}$ inhibition layer formed at the steel/coating interface during hot dipping. The results clearly show that Al in the liquid Zn bath can reduce the crystalline $_{C-X}MnO.SiO_{2}$ (x>1) oxides but not the amorphous $_{a-X}MnO.SiO_{2}$ (x<0.9) and $a-SiO_{2}$ oxides. These oxides remain embedded in the Zn layer or in the inhibition layer, making it possible to apply a Zn or Zn-alloy coating on martensitic steel by hot dipping. The hot dipping process was also found to deteriorate the mechanical properties, independently of the Zn bath composition.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2012.10a
• /
• pp.117-118
• /
• 2012

• Corrosion Science and Technology
• /
• v.23 no.2
• /
• pp.83-92
• /
• 2024

A hot-dip simulator was utilized to replicate abnormal coating buildup observed during line stops at galvanize lines, assessing the influence of processing conditions on buildup (up to 14 mm/side). Steel samples from 19 coils (comprising IF, BH, LCAK, HSLA, DP600-DP1180, Si: 0.006 - 0.8 wt%, P: 0.009 - 0.045 wt%) were examined to explore the phenomenon of heavy coating growth. It was discovered that heavy coating buildup (~3 mm/h) and rapid strip dissolution (~0.17 mm/h) in a GA or GI pot can manifest with specific combinations of steel chemistry and processing conditions. The results reveal the formation of a unique coating microstructure, characterized by a blend of bulky Zeta crystals and free Zn pockets/networks due to the "Sandlin" growth mechanism. Key variables contributing to abnormal coating growth include steel Si content, anneal temperature, dew point in heating and soaking furnaces, Zn pot temperature, Zn bath Al%, and cold-rolling reduction%. At ArcelorMittal Dofasco galvanize lines, an automatic online warning system for operators and special scheduling for incoming Si-bearing steels have been implemented, effectively preventing further heavy buildup occurrences.

• Transactions on Electrical and Electronic Materials
• /
• v.4 no.3
• /
• pp.15-18
• /
• 2003

Aluminum oxide ($Al_2O_3$) materials were coated conformally on ZnO nanorods by atomic layer deposition (ALD). The ZnO nanorods were first synthesized on a Si(100) substrate from ball-milled ZnO powders by a thermal evaporation procedure. $Al_2O_3$ films were then deposited on these ZnO nanorods by ALD at a substrate temperature of $300^{\circ}C$ using trimethylaluminum (TMA) and distilled water ($H_2O$). Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) images of the deposited ZnO nanorods revealed that amorphous $Al_2O_3$ cylindrical shells surround the ZnO nanorods. These TEM images illustrate that ALD has an excellent capability to coat any shape of nanorods conformally.

• Metals and materials international
• /
• v.24 no.6
• /
• pp.1241-1248
• /
• 2018

The reactive wetting behaviors of molten Zn-Al-Mg alloys on MnO- and amorphous (a-) $SiO_2$-covered steel sheets were investigated by the sessile drop method, as a function of the Al and Mg contents in the alloys. The sessile drop tests were carried out at $460^{\circ}C$ and the variation in the contact angles (${\theta}_c$) of alloys containing 0.2-2.5 wt% Al and 0-3.0 wt% Mg was monitored for 20 s. For all the alloys, the MnO-covered steel substrate exhibited reactive wetting whereas the $a-SiO_2$-covered steel exhibited nonreactive, nonwetting (${\theta}_c>90^{\circ}$) behavior. The MnO layer was rapidly removed by Al and Mg contained in the alloys. The wetting of the MnO-covered steel sheet significantly improved upon increasing the Mg content but decreased upon increasing the Al content, indicating that the surface tension of the alloy droplet is the main factor controlling its wettability. Although the reactions of Al and Mg in molten alloys with the $a-SiO_2$ layer were found to be sluggish, the wettability of Zn-Al-Mg alloys on the $a-SiO_2$ layer improved upon increasing the Al and Mg contents. These results suggest that the wetting of advanced high-strength steel sheets, the surface oxide layer of which consists of a mixture of MnO and $SiO_2$, with Zn-Al-Mg alloys could be most effectively improved by increasing the Mg content of the alloys.