• 한국세라믹학회지
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• 제47권3호
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• pp.256-261
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• 2010

Physical properties of Plasma electrolytic oxidized 8 different types of Al alloys, A-1100, A-2024, A-5052, A-6061, A-6063, A-7075, ACD-7B and ACD-12 were investigated. The electrolyte for PEO was $Na_2SiO_3$ solutions with NaOH and some alkali earthen metal salts. Porous layer near the surface of PEO coating was not found, and surface roughness Ra50 was below 2.5 ${\mu}m$. Surface roughness was affected by growth rate of plasma electrolytic oxidized layer, not by Si content in Al alloy.

• 한국군사과학기술학회지
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• 제14권5호
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• pp.897-903
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• 2011

The objective of this study is to investigate the thermal behavior on material surface and the variation in the surface morphology of aluminum 6061 alloy by the Nd:YAG pulsed-laser irradiation. First, we predicted the surface temperature variation during pulsed-laser irradiation by using the two dimensional finite element analysis. When the pulsed-laser of 133 mJ energy and 5 ns pulse duration is irradiated on the surface of aluminum alloy, the material surface is thought to be melting because the surface temperature rises steadily up to about $660^{\circ}C$ exceeding the melting point. Also, the experimental results show that the solidification microstructure has been developed clearly after surface melting. Second, the diameter of melted zone was analysed by finite element analysis and measured by OM(Optical Microscopy). It increased logarithmically with increase in the number of laser irradiation. In addition, AFM(Atomic Force Microscopy) measurement showed an increase in the average surface roughness during pulsed-laser irradiation.

• 한국세라믹학회지
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• 제47권4호
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• pp.283-289
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• 2010

Physical properties of Plasma electrolytic oxidized 8 different kinds of Al alloys, A-1100, A-2024, A-5052, A-6061, A-6063, A-7075, ACD-7B and ACD-12 were investigated. The electrolyte for PEO was $Na_2SiO_3$ and NaOH and some alkali earthen metal salts system solution. $\eta$-alumina, as well as $\gamma$-alumina, was main crystal phase, which were ever reported. Also, $Al_{4.95}Si_{1.05}O_{9.52}$ was found only in this research. So we can conclude that the process conditions of PEO apparatus and composition and concentration of its electrolyte affects crystal structure and physical properties of PEO layers much more than the compositions of Al alloy.

• 한국주조공학회지
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• 제37권2호
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• pp.38-44
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• 2017

Given that the conventional extrusion of high-strength Al alloys such as 7075 aluminum alloys is difficult due to their very low extrudability as compared to that of 6061 aluminum alloys, thixo-extrusion can be used to obtain a high-strength material easily at a lower extrusion pressure as compared to conventional extrusion. In this study, hot- and thixo-extruded 7075 aluminum alloys are prepared by a vertical forward extrusion process and their microstructures, hardness levels, and compressive properties are investigated. Hot-extruded alloy bars are assessed to obtain a microstructure elongated in the extrusion direction, whereas with thixo-extruded alloy bars, it was possible to obtain a microstructure having fine and equiaxed grains by dynamic recrystallization. The resulting isotropy and improved formability at the hot deformation temperature of the thixo-extruded alloy were attributed to the fine and equiaxed grains formed by the thixo-extrusion process.

• 한국재료학회지
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• 제17권4호
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• pp.192-197
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• 2007

The effects of immersion time in the liquid nitrogen on the behavior of aluminum alloys used for the hydrogen storage tank of auto-mobile at cryogenic temperature were investigated. With increasing immersion time in the liquid nitrogen, the elongation of AI 5083 alloy at cryogenic temperature decreased because of non-uniform fracture of precipitates on the grain boundary, and the serration also occurred because of discontinuous slip due to rapid decreasing of the specific heat. The mechanical properties of AI 6061 alloy at cryogenic temperature were characterized by uniformed yield strength, tensile strength and elongation regardless of the immersion time in the liquid nitrogen. These mechanical properties of aluminum alloys at cryogenic temperature were interpreted by the strength of grain boundary and the slip deformation behavior.

• 한국표면공학회지
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• 제52권4호
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• pp.203-210
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• 2019

In this work, anodizing behavior of 6xxx series aluminum alloys was studied under constant current density and constant voltage conditions in 20% sulfuric acid solution by V-t curves, I-t curves, thickness measurement, observations of surface appearance and cross-sectional observation of anodizing films. The film growth rate of the anodizing films on Al6063, Al6061 and Al6082 obtained at 20 V were $0.63{\mu}m/min$. $0.46{\mu}m/min$ and $0.38{\mu}m/min$, respectively. Time to the initiation of imperfections at the oxide/substrate interface under constant current condition was shortened and colors of anodizing films became darker with the amount of alloying elements in 6xxx series aluminum alloys. Based upon the experimental results obtained in this work, it is concluded that maximum anodizing film thickness without interfacial defects is reduced with increasing amount of alloying elements and brighter anodizing films can be obtained by decreasing amount of alloying elements in the aluminum alloys.

• Design & Manufacturing
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• 제14권4호
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• pp.46-51
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• 2020

The purpose of this study was to analyze the change in tensile strength characteristics of the weld when the welding speed and rotational speed of the tool, which are representative variables of the friction stir welding process. The equipment used in the experiment was Machining Center No. 5. The material used in the experiment is an AA6061-T6 alloy, and a rolled plate with a thickness of 2mm was used. Two experimental variables were selected, the welding speed of the tool and the rotational speed of the tool. The experimental conditions were selected in the range in which a healthy weld could be obtained through a preliminary experiment. The welding speed of the tool was increased to 100mm/min, 200mm/min, and 300mm/min, and the rotational speed of the tool was increased to 1000rpm, 2000rpm, and 3000rpm. As a result of the experiment, the tensile strength increased as the rotational speed of the tool changed at each tool welding speed. In addition, as the welding speed of the tool increased, the tensile strength of the weld was increased. The condition with the highest tensile strength of the weld was found to be a tool feed speed of 300 mm/min and a tool rotation speed of 3000rpm.

• 한국분말재료학회지
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• 제30권3호
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• pp.255-261
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• 2023

Aluminum alloys are widely utilized in diverse industries, such as automobiles, aerospace, and architecture, owing to their high specific strength and resistance to oxidation. However, to meet the increasing demands of the industry, it is necessary to design new aluminum alloys with excellent properties. Thus, a new method is required to efficiently test additively manufactured aluminum alloys with various compositions within a short period during the alloy design process. In this study, a combinatory approach using a direct energy deposition system for metal 3D printing process with a dual feeder was employed. Two types of aluminum alloy powders, namely Al6061 and Al-12Cu, were utilized for the combinatory test conducted through 3D printing. Twelve types of Al-Si-Cu-Mg alloys were manufactured during this combinatory test, and the relationship between their microstructures and properties was investigated.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2009년 추계학술발표대회
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• pp.67-67
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• 2009

알루미늄 합금 재질은 무게의 경량화와 기계적강도가 우수하며 다른 비철금속에 비하여 값이 저렴한 장점이 있다. 현재 산업현장에서 활용하는 가장 흔한 접합법으로 TIG, RSW 등과 같은 용융 용접법을 현재는 많이 사용 하고 있지만 열전도도가 높아 열 확산이 빠르고, 이에 따라 모재의 팽창이 일어나 열변형을 유발하며, 산화피막은 그 내부에 함유된 결정수가 아크용접 중 분해되어 수소를 방출함으로 기공이 발생하여 부도체로 저항용접시 전도성을 방해하는 등의 문제를 발생시킨다. 또한 철에 비해 4배정도 큰 전기전도율에 따라 저항용접시 대전류를 사용해야 하는 등의 문제점이 발생하고 있다. 이와 같은 알루미늄 합금의 용융용접 과정에서 발생하는 단점을 극복하는 기술로 고상접합 방법인 마찰교반용접법(Friction Stir Welding)이 활용되고 있다. FSW는 1991년 영국의 TWI에서 개발된 최신 용접법으로 모재를 용융점 아래에서 고상용접시키는 방법으로 용융에 따른 열변형과 흄가스(hume gas)와 스패터(spatter)를 억제시켜 주는 친환경적인 용접법이다. 이러한 마찰교반용접의 기술은 그동안 특허에 따른 로열티가 산업현장에서 사용하는데 문제가 되었으나 특허보호 기간인 20년이 1년정도의 기간밖에 남지 않은 상황에서 그 사용은 날로 증가하리라 본다. 이러한 마찰교반용접부의 결함을 평가하는 방법에는 UT, RT 등이 활용되고 있으나 얇은 박판에서의 결함검출은 용이하지 않다. 이리한 문제점을 해결하기위하여 초음파 가진을 이용한 적외선 열화상 검출 기법을 이용하여 마찰교반용접부의 결함 검출 가능성을 연구하였다. 20kHz의 주파수를 400Watt로 가진시켜 겹치기(lap joint) 마찰교반용접이된 A6061-T6의 용접부에 초음파를 입사하였을 때 발생하는 열을 적외선 열화상 카메라를 이용하여 측정함으로써 마찰교반겹치기 용접부의 결함 검출에 활용하였다. 용접부에 초음파를 입사하였을 때 부분적으로 온도차이가 발생하였고, 그에 따른 열화상을 검출 할 수 있었다. 이러한 열화상과 실제 시험편의 용접부의 강도를 평가하기 위하여 인장시험을 하였다. 그 결과 초음파 적외선 열화상 검출에서 발열부위가 나타난 부분이 인장시험에서 낮은 인장강도를 보였다.

• 대한기계학회논문집A
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• 제34권12호
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• pp.1877-1883
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• 2010

선배열 슬릿 마스크를 이용하여 발생시킨 협대역의 레이저 여기 표면파의 주파수 특성을 이론적으로 분석하여 음향비선형성 분석에 영향을 미칠 수 있는 초기 고조파성분의 발생 기구를 규명하였다. 그리고 알루미늄 6061-T6 합금의 음향 비선형성에 대한 슬릿 열림폭과 레이저 세기의 영향을 단일 슬릿과 선배열 슬릿을 이용하여 실험적으로 분석하였다. 고조파 성분의 진폭은 슬릿 열림폭에 의존하는데 본 연구의 경우 슬릿 배열간격을 1.67 mm로 하여 1.75 MHz의 표면파를 발생시켰으며 이 경우 슬릿 열림폭이 0.5 mm에서 1.0 mm로 증가함에 따라 2차 고조파 성분의 진폭은 약 80 % 감소하였다. 또한 레이저 세기에 따라서 기본파 성분 진폭($A_1$)을 변화시키면서 2차 고조파 진폭($A_2$)의 변화를 실험한 결과 $A_1^2$과 $A_2$간에는 우수한 선형 관계를 보였으며, 이는 전형적인 음향비선형성의 특징을 잘 나타낸다.