• Journal of the Korean institute of surface engineering
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• v.32 no.2
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• pp.134-143
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• 1999

The effects of silicon on galvannealing behavior of interstitial-free (IF) steels were studied. The growth rate of the Fe-Zn alloy layer was retarded as silicon in the steel added. Titanium in steel strongly favors Fe-Zn reaction, in particular outburst structures, whereas silicon inhibit them. Cross-sectional and planar views of galvannealed coatings were investigated to characterize alloy phase development. A possible mechanism to explain the retardation effect of silicon is discussed in terms of concentration on surface and inhibition layer.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.182-182
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• 2016

철강은 기본적으로 강도가 우수하고 그 매장량이 풍부할 뿐만 아니라 대량생산이 가능하다 또한 다른 금속과 합금을 구성하여 또 다른 특성을 부여할 수 있기 때문에 현재 전 세계 금속 생산량의 95%를 차지할 정도로 많이 사용되며, 각종 산업과 기술이 발달함에 따라 그 중요도는 점점 더 커져가고 있다. 하지만 철강은 사용 환경 중 부식에 의해 그 수명과 성능이 급격히 저하되기 때문에 내식성을 향상시키기 위하여 도장이나 도금 등의 표면처리를 포함한 다양한 방법이 적용되고 있다. 그 중 철강재의 도금 표면처리방법은 주로 아연을 이용한 용융도금이나 전기도금 등과 같은 습식 프로세스가 널리 사용되고 있다. 여기서 아연은 철보다 이온화 경향은 크나 대기 환경 중 산소와 물과 반응하여 Zn(OH)2와 같은 화합물을 형성함으로써 철강재 표면상 부식인자를 차단(Barrier)함은 물론 사용 중 철 모재가 노출되는 결함이 발생하는 경우에는 철을 대신하여 희생양극(Sacrificial Anode) 역할을 하기 때문에 철의 부식방식용 금속으로 가장 많이 사용되고 있다. 한편 최근에는 철강의 사용 환경이 다양해짐은 물론 가혹해지고 있어서 이에 따른 내식성 향상이 계속해서 요구되고 있는 추세이다. 따라서 본 연구에서는 철강재의 내식성을 향상시키기 위한 일환으로 현재 많이 사용되고 있는 용융아연도금 강판 상에 아연보다 활성이 높은 마그네슘(Mg)을 건식 프로세스 방법 중에 하나인 PVD(Physical Vapour Deposition)법에 의해 코팅하는 것을 시도하였다. 일반적으로 PVD법에 의해 진공증착하는 경우에는 그 도입가스로써 불활성가스인 아르곤(Ar)을 사용하는 경우가 대부분이나 여기서는 상대적으로 비활성이면서 그 크기가 작은 질소(N2)가스를 도입하여 그 증착 막의 몰포로지는 물론 결정구조도 제어하여 그 내식특성을 향상시키고자 하였다. 본 연구에서는 철강재의 내식성을 향상시키기 위한 방법으로 마그네슘(Mg)를 PVD(Physical Vapor Deposition)법 중 진공증착법(Vacuum Deposition)을 사용하여 용융아연도금 강판 상에 마그네슘 증착 막을 형성하였다. 즉, 여기서는 진공증착 중 질소(Nitrogen, N2)가스를 도입하여 진공챔버(Vacuum Chamber)내의 진공도를 $1{\times}10^{-1}$, $1{\times}10^{-2}$, $1{\times}10^{-3}$, $1{\times}10^{-4}$로 조절하며 제작하였다. 또한 제작된 시편에 대해서는 SEM(Scanning Electron Microscope) 및 XRD(X-Ray Diffraction)을 사용하여 형성된 아연도금상 마그네슘 막의 표면 몰포로지 및 결정구조의 변화를 분석함은 물론 침지시험, 염수분무시험, 분극시험을 통해 이 막들에 대한 내식특성을 분석 평가하였다. 상기 실험결과에 의하면, 진공 가스압이 증가됨에 따라 마그네슘 막의 두께는 감소하였으며, 그 몰포로지의 단면은 주상정(Columnar)에서 입상정(Granular) 구조로 변화하며 표면의 결정립은 점점 미세화 되는 경향을 나타냈다. 이때의 표면의 결정배향성(Crystal orientation)은 표면에너지가 상대적으로 큰 면이 우세하게 나타나는 경향이 있었다. 또한 본 실험에서 형성한 진공증착 막은 비교재인 용융아연도금강판보다 우수한 내식성을 나타냈고, 본 형성 막 중에는 마그네슘 막 두께가 작음에도 불구하고 질소 가스압이 가장 큰 조건일수록 내식성이 우수한 경향을 나타냈다. 이상의 결과는 철강재의 내식성 향상을 위한 응용표면처리설계에 기초적인 지침을 제공할 수 있을 것으로 기대된다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2015.11a
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• pp.142-142
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• 2015

아연-마그네슘 합금은 마그네슘 첨가로 인한 뛰어난 내식성과 아연의 자원 고갈에 대한 갈등을 해소할 수 있다는 장점을 가지고 있으므로 차세대 강판 도금 소재로서 주목받고 있다. 그러나 아연-마그네슘의 도금 공정은 상대적으로 높은 융점을 지닌 마그네슘 첨가로 인해 기존의 아연 도금 공정에 비해 고온에서 이루어지므로 용융 금속에 의한 도금 설비의 빠른 손상이 발생하게 된다. 따라서 이와 같이 고온 환경에서도 사용 가능한 수준의 내구성을 지닌 소재의 개발이 반드시 필요한 상황이다. 선행 연구에 의하면 Mo은 아연-마그네슘 용탕에서 우수한 내침식 특성을 보이는 것으로 확인되었지만 pure Mo의 경우 고온 산화에 취약한 단점을 가지고 있어 내구성에 한계를 보인다. 따라서 본 연구에서는 이러한 문제를 해결하기 위해 pack cementation 공정을 통해 Mo 표면에 내산화 특성이 우수한 Mo 금속간화합물($MoSi_2$, $Mo_3Si$, $Mo_5SiB_2$)을 형성시켰고 이를 대상으로 아연-마그네슘 용탕에 대한 내산화 거동을 평가하였다.

• Journal of the Korean institute of surface engineering
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• v.28 no.1
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• pp.14-22
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• 1995

The effects of iron content in coated layer, surface roughness and lubricants on the formability of commercial Zn-Fe alloy electroplated steel sheets used for automotive bodies were investigated. The higher the iron content in deposit, the lower the friction coefficient of Zn-Fe alloy electroplated steel sheets. The surface roughness of coated layer hardly influenced the frictional characteristics. The formability of Zn-Fe alloy electroplated steel sheets was found to be more affected by the lubricant than by iron content in Zn-Fe alloy electrodeposit.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.6
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• pp.560-567
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• 2009

This paper was designed to estimate the adhesion strength of galvannealed coatings on steel sheets. The adhesion strength were evaluated using single lap - shear tests where the lap joint was bonded by structural adhesive. Tests were performed for overlap length of 5mm, 10mm and 15 mm and three directions (0, 45, 90) of steel sheets used as the adherend of the overlap joint. After the tests, FE simulations of the single lap-shear test were also carried out to observe the stress distribution in the interface between the adhesive and the coated sheet. The results showed that the joint failure loads obtained from the tensile tests of bonded single lap-joints were the same, regardless of overlap lengths and directions of steel sheets. Also, the failure of galvannealed coatings greatly depended on shear stress distribution in the interface and the value was about 30MPa.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.238-243
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• 2007

This paper is designed to estimate the adhesion strength of coating layer on galvannealed steel sheet using lap shear test. The single lap shear test is the most commonly used standard test for determining the strength of medium-strength and high strength bonds. The bond strength of bonded single lap joints on subjecting the substrates to loads is determined by lap shear forces in the direction of the bonded joint. In this study, specimen for adhesion strength test was made to attach coated sheet to cold rolled sheet and were heated in temperature of 180 for 20minutes. After test, detached parts of coatings on coated sheet were observed using SEM and EDX to identify substrate and complete detachment. The tested results showed that adhesive strength of coating is unrelated to anisotropy of sheet and is difficult to be extracted using conventional theory because of fine cracks of coating layers which were created during annealing process.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1997.10a
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• pp.310-315
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• 1997

An extensive corrosion study was initiated by galvalume steel sheet manufacturing company to clarify the corrosion behavior of zinc and zinc and zinc-alloy coated automotive sheet steel in out panel and electrical application. Since the early 1980's the use of zinc and aluminum alloy coated steel for vehicular corrosion protection has increased drastically. This paper describes the evaluation of formability, weldability and painted corrosion performance of galvalume steel sheet. This paper presents an overview of the program and some initial test results on the weldability, lifetime of the electrode tip shape of the spot welding and corrosion protection. Galvalume steel sheet improved corrosion performance and spot weldability of galvalume steel has no problem for the variation of welding current. And tip lifetime was changed according to the influence of shape.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.389-392
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• 2005

In the modern days, a galvannealed sheet steel(GA) instead of a cold rolled steel sheet has been widely used as an alternative to extend the life of automotive body. Accordingly, the mechanical properties of GA for automobiles were taken Into account and studied by comparing with the temperature variation on annealing in this study. To clarify the effect of surface features in the mechanical properties of GA, the several tests such as nanoindentation and FE-analysis were executed. For this goal use is made of the method of neural networks. The developed neural networks apply also to obtain reliable mechanical properties of the thin films. Load-displacement curve was computed by the analysis procedure and compared with experimental results.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.215-222
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• 2007

Coating of Hot-dip galvannealed steel consists of various Fe-Zn intermetallic compounds. Since the coating is hard and there for is very brittle, the surface of steel sheet is easy to be ruptured during second manufacturing processing. This is called as powdering. In addition, forming equipment might be polluted with debris by powdering. Therefore, various research have been carried out to prohibit powdering fur improving the quality of GA steel. This paper carried out finite element analysis combined with damage model which simulate the failure of local layer of hot-dip galvannealed steel surface during v-bending test. Since the mechanical property of intermetallic compound was unknown exactly, we used the properties calculated from measurements. The specimen was divided into substrate, coating layer and interface layer. Local failure at coating layer or interface layer was simulated when elemental strain reached a prescribed strain.

• Corrosion Science and Technology
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• v.21 no.3
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• pp.221-229
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• 2022

To understand effects of cooling rates of coating layer on microstructures and corrosion behaviors of hot-dip alloy coated steel sheets (Zn-5%Al-2%Mg) in a neutral aqueous condition with chloride ion, a range of experimental and analytical methods were used in this study. Results showed that a faster cooling rate during solidification decreased the fraction of primary Zn, and increased the fraction of Zn-Al phase. In addition, interlamellar spacing became refined under a faster cooling rate. These modifications of the coating structure had higher open circuit potentials (OCP) with smaller anodic and cathodic current densities in the electrochemical potentiodynamic polarization. Surface analyses after a salt spray test showed that the increase in the Zn-Al phase in the coating formed under a faster cooling rate might have contributed to the formation of simonkolleite (Zn₅(OH)₈Cl₂·H₂O) and hydrotalcite (ZnAl₂(OH)₆Cl₂·H₂O) with a protective nature on the corroded outer surface, thus delaying the formation of red rust.