• 한국표면공학회지
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• 제34권4호
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• pp.313-320
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• 2001

It is well known that the amount of hot-dip Zn coated sheet steels used for automotive is rapidly increasing. As hot-dip steel sheets show good corrosion resistance and excellent formability, the demand for outer panel of automotive has been increased in order to satisfy with the requirement of high surface qualify. There are many kinds of factors influencing on the surface quality and the dross control in the galvanising bath is regarded as one of the most important thing. In this study the characteristic and growing behavior of dross in the galvanizing bath were investigated and the effect of dross on the surface defect of GA was surveyed. The dross defects on the GA sheet steels result from bottom dross whose diameter are larger 50$\mu\textrm{m}$ in the Zn pot. Dross-free state exist for about 30 hours from starting time of GA production.

• 한국표면공학회지
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• 제34권4호
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• pp.327-336
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• 2001

The skinpassing conditions such as roll type, roll force and roll roughness of the work roll were evaluated to give the surface properties of the galvanized steel sheets that were required for automotive and to get rid of the surface defects that caused with the bad control of galvanized coating process parameters. The surface defects of the galvanized steel sheets such as the ripple mark and the scratch were completely removed as the roll force of SPM work roll was increased and the amount of the transfer of roll surface texture to the strip was also gained a lot. The image clarity of electro discharge textured (EDT) coated steel sheets before and after painting was higher than that of the bright (BRT) and shot blasted (SBT) coated steel sheets because of higher PPI value, lower waviness and uniform surface pattern. Since micro-craters transferred on the surface of the galvanized steel sheets played a role of nucleation sites of chromate reaction, Increase of micro-craters was bring to better corrosion resistance with the increase of the roll force and the use of EDT roll at the skin pass mill.

• 대한금속재료학회지
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• 제49권11호
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• pp.831-838
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• 2011

Effects of spangle size and crystallographic characteristics on the surface appearance, galling properties, and adhesive strength of hot-dip galvanized steel sheets have been investigated. Both spangle size and crystallographic orientation measured by optical microscopy, scanning electron microscopy, and X-ray diffraction were identified as critical factors influencing the galvanized coating performance. By decreasing the spangle size, surface appearance and galling properties related to the friction coefficient were significantly improved. However, low temperature adhesive-strength with small spangle galvanized steel sheets showed lower values compared to commercially used galvanized coating. The variation of adhesive strength in terms of spangle size has been clarified.

• 한국표면공학회지
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• 제32권2호
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• pp.157-164
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• 1999

In this study the effect of nickel addition on the coating weight of mini-mill steels containing silicon has been studied. It is shown that the pure zinc accelerated growth of the alloy layers occurred by a rapid growth of the zeta phase at 0.06%Si. The addition of 0.06%Ni to a pure zinc bath was found to be very effective in reducing the coating weight and promoting preferential development of the delta phase. The coating obtained by immersion in the Zn-Ni bath shows the presence of a nickel-rich region between the zeta phase and the eta phase. It is suggested that nickel prevents the rapid growth of the zeta phase due to the formation of the Zn-Ni-Fe ternary compound, which may act as a barrier to inward diffusion of zinc or iron at the zeta-eta boundary.

• 한국표면공학회지
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• 제31권6호
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• pp.371-378
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• 1998

The zind bate contaminated in the hot dip galvannealed operation was successfully by appling the dross formation mechanism ; the Fe content was lowered from 0.028% to 0.011% and the dress size was decreased from 15~20$\mu\textrm{m}$ to under 3$\mu\textrm{m}$. The cooled metal from CGL zinc bath during operation of the galvannealed steel strip was remelted in graphite crucible at the lab and agitated after increasing Al content from 0.14% to 0.16% with decreasing the molten metal temperature from $470^{\circ}C$to $445^{\circ}C$. The agitating was done by agitator and nitrogen. The molten was analyed by SEM and EDS. It was considered that the Fe and the bottom dross($FeZN_7$) could react with aluminium to from the float dress($Fe_2Al_5$) according to the molten metal temperature down and the float dress rise to the surface of the zine bath. So the Fe and dross in the bath could be romoved out of the bath. It was confirmed that the proper purication conditions of GA zine bath is 0.02% of Al increasing, bath temperature down from $460^{\circ}C$ to $450^{\circ}C$and agitator and nitrogen.

• 한국표면공학회지
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• 제34권3호
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• pp.206-214
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• 2001

The purpose of this study is to determine the effects of Ni on precipitate formation in a Ni added galvanizing bath, which has various Ni content from 0.03wt.% to 0.5wt.%. The addition of hi in the Ni containing galvanizing bath resulted in the formation of Al-Ni intermetallic compounds such as $Al_3$$Ni_2$ and $Al_2$Ni, which make up most of the top precipitates. At 0.07wt.%Ni, Al-Ni intermetallic compound formed sensitively with small amount of Al addition. By analysing the reaction thickness of galvanized steel, it was found that Ni addition in a Zn-0.18w1.%Al bath tended to suppress the formation of Fe-Zn intermetallic compounds but the formation of these compounds increased with increasing Ni concentration above 0.1wt.%.

• 한국수산과학회지
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• 제50권4호
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• pp.388-395
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• 2017

We investigated the toxicity of zinc and aluminum hot-dip galvanized sheet steel to abalone Haliotis discus hannai via changes in the gill and hepatopancreas using histological and transmission electron microscopy analysis. Experimental groups were composed of one control and four exposure conditions (direct or indirect exposure to zinc and aluminum hot-dip galvanized sheet steel). In the control group, aluminum exposure groups (direct and indirect), and indirect zinc exposure group, abalone mortality was not observed until the end of the experiment, and no histopathological changes were observed in the gill and hepatopancreas. However, the direct zinc exposure group exhibited 100% mortality. Ultrastructural analysis of the cytoplasm of ciliated and microvilli-bearing epithelial cells from gill filaments revealed electron-dense vesicles near the cell membrane and disruption of the nuclear membrane. We also observed swollen mitochondria and a loss of mitochondrial cristae. The hepatopancreas showed similar changes, and we detected highly electron-dense particles within the vesicles. These results suggest that abalone exposed directly to zinc hot-dip galvanized sheet steel experience acute toxicity, causing damage to cell organelles in the gill and hepatopancreas and, finally, inducing mortality.

• 한국재료학회지
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• 제16권2호
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• pp.129-136
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• 2006

In order to get basic information on the reference electrode material for the long life Al concentration sensor in zinc galvanizing melt, the workability and stability of fluorine potential cell with $CaF_2$ single crystal electrolyte were examined carefully at constant temperature for six kinds of reference materials (Zn, Sn, Cd, Bi, Pb, Al-Sn alloy + fluorides). Good workability and stability of the sensor were found in sensor with $Bi+BiF_3$ reference electrode. The Al sensor with $Bi+BiF_3$ reference electrode was assembled and was tested in Zn-Al melt with different Al concentration. The EMF was changed rapidly with the change of Al concentration and was stabilized in a short time. Thus the response of EMF was satisfactory for $CaF_2$ sensor. The correlationship between EMF from the sensor and logarithm of Al concentration has been derived from the least square regression method. E/mV=57.515log[wt% Al]+1883.3 R=0.9717 ($0.013{\leq}[wt% Al]{\leq}0.984$) The EMF from Al sensor was increased linearly against logarithm of [wt% Al]. The fluorine potential of Zn-Al melt was also calculated to be in the range of $10^{-60}{\sim}10^{-61}$ Pa for the present experiemental condition.

• 한국표면공학회지
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• 제20권4호
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• pp.144-153
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• 1987

In the case of dipping the Ni-Resist cast iron into molten aluminum with iron content, the thickness of intermetallic compound was remarkably increased with increasing iron content. The thickness was shown by following equation in the range of 1-3% iron content; $x=22.5t^{1/2}+4.47{\cdot}t{\cdot}(Fe%)$. where, x is thickness(${\mu}m$), t the time (minute), Fe% the iron w/o. When the Ni-Resist cast iron was dipped into the molten aluminum containing zinc content, the intermetallic compound thickness was also increased with increasing zinc contents. And thickness was represented by the following equation in the range of 2-10% zinc content; $x=3.46t^{1/2}+0.27{\cdot}t{\cdot}(Zn%)$. However, in the case of dipping the Ni-resist cast iron into molten aluminum with silicon content, the thickness of intermetallic compound was decreased with increasing silicon content, as shown in the following equation; $x=7.17t^{1/2}-0.15{\cdot}t{\cdot}(Si%)$. The intermetallic compound formed onto Ni-Resist cast iron was identified to be $FeAl_3\;and\;Fe_3Al$. As the result of hardness measurement, the peak hardness appeared in the intermetallic compound at near interface of the cast iron and the compound.

• 한국기계기술학회지
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• 제20권6호
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• pp.886-893
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• 2018

In this study, clinching characteristics of aluminum and galvanized steels were investigated for the application of clinching as a joining technique to aluminum wheelhouse assembly. A6451 aluminium alloy and galvanized steel sheets were joined by hybrid joining(clinching + adhesive bonding). Tensile-shear load and fracture mode of hybrid joints were investigated. Maximum tensile-shear load of hybrid joints was about six times higher than that of clinched joints without adhesive. Energy absorption values of hybrid joints were higher than those of clinched joints without adhesive as well as resistance spot welded steel joints. Developed aluminum wheelhouse assembly showed higher static stiffness than the existing steel parts. Aluminum wheelhouse inner panel unit was 44% lighter than the steel unit, and the final assembled aluminum wheelhouse was 14.6% lighter than the existing steel parts.