• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.2
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• pp.104-109
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• 2010

Lap joint friction stir welding(LFSW) is an relatively new solid state joining process. A6061-T6 aluminium alloy has gathered wide acceptance in the fabrication of light weight structures requiring a high strength to weight ratio and good corrosion resistance. Test methods used in this paper, lock-in thermography, a phase difference between the defect area and the healthy area indicates the qualitative location and size of the defect. In this paper, the defects detected from the thermal image of mechanical properties for weld were evaluated and compared by the lock-in infrared thermography technique.

• Proceedings of the KWS Conference
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• 2004.05a
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• pp.156-158
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• 2004

The microstructural evolution in a 304 stainless steel weld during FSW was examined. The SZ and TMAZ showed typical dynamically recrystallized and recovered microstructures, respectively, The microstructural observation revealed that sigma phase was formed at the advancing side of the stir zone. A possibility was suggested that the rapid formation of the sigma phase is related to the transformation of austenite to delta-ferrite in the stir zone, from introduction of high strain and dynamic recrystallization during FSW.

• Proceedings of the KWS Conference
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• 2005.11a
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• pp.135-137
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• 2005

The body of the work covers FSW welding of Al6061 and its thermal distribution based on an analytical model for the heat input at the probe/matrix boundary of Al plates and FSW tool due to the effect of combined translation and rotational motion of the tool pin and shoulder. Finally the 2D- finite element heat transfer analysis program has been used to plot the heat distribution at the Friction Stir Welded joint in Al 6061 plate. The work concludes that the heat distribution result obtained from FE analysis has a reasonable agreement with the experimentally measured values.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.223-225
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• 2005

In order to demonstrate the friction stir weldability of the Al 6061 T-6 unequal thickness joint and determine optimum welding parameters, the relations between welding parameters and properties of the joints have been studied in this paper. The experimental results showed that the tensile properties of the joints are affected by the welding heat inputs and tool shape. In this study, the maximum ultimate strength of the as-welded joint is equivalent to 78% and 18hour aged joint is equivalent to 93% that of the base metal. Though the voids-free joints are fractured at the thermally affected zone on the advancing side, the fracture occurs at the weld center when the void defects exist in the joints.

• Corrosion Science and Technology
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• v.6 no.1
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• pp.33-35
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• 2007

Welding technology plays an important role in the fabrication of structure, and this has led to an increasing attention in the use of high quality advanced welding technology such as power beam welding, friction stir welding, and laser-arc hybrid welding, etc. At the same time, welding can influence various factors in the performance of plant and equipment, and corrosion behaviour of weldment has been one of the major issues for both welding and corrosion research engineers. The aim of this paper is to give a short survey of the recent technical trends of welding and corrosion behaviours including the electrochemical corrosion, stress corrosion cracking, and corrosion fatigue in connection with the welding materials, welding process, and welding fabrication.

• Journal of Advanced Marine Engineering and Technology
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• v.7 no.1
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• pp.23-33
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• 1983

경제성과 압접성능의 우수성 때문에 일반 산업기계, 방위산업기계 및 우주항공기계등의 부품생산에 응용되고 있는 마찰 용접에 있어서, 현재 주 관심사 중의 하나는 용접강도에 대한 신뢰성 높은 공정중 비파괴 검출이며 이들의 실용화를 위한 정량적 해석이다. 그러나 이러한 연구는 아직 개발 완성되지 못하고 있다. 본 연구에서는, AE법에 의한 용접강도의 공정중 비파괴적 QC시스템 개발을 최종 목적으로 한 설계자료를 얻기 위하여, 이종강의 봉과 봉, 관과 관의 마찰용접강도와 AE 총누적량에 용접조건이 미치는 영향이 실험적으로 조사되었고, 회전 속도를 매개 변수로 하여 용접강도와 AE 총누적량과의 정량관계가 수립되었다.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.3
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• pp.273-278
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• 2012

The use of Al alloys instead of fiber-reinforced plastic(FRP) in ship construction has increased because of the advantages of Al-alloy ships, including high speed, increased load capacity, and ease of recycling. This paper describes the effects of probe diameter on the optimum friction stir welding conditions of 5456-H116 alloy for leisure ship, measured by a tensile test. In friction stir welding using a probe diameter of 5 mm under various travel and rotation speed conditions, the best performance was achieved with a travel speed of 61 mm/min. Using a probe diameter of 6 mm, rotation speeds of 170-210 rpm, and a travel speed of 15 mm/min produced a rough surface and voids because of insufficient heat input produced by the low rotation speed. At 500-800 rpm, chips were observed, although there were no voids, and the weld surface was excellent. However, at 1100-2500 rpm, many chips were produced due to excessive heat input. Heat effects were very evident on the bottom. For a travel speed of 15 mm/min, heat input caused by friction increased as the rotation speed increased. The mechanical characteristics were degraded by accelerated softening due to increasing heat input.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.7
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• pp.434-441
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• 2016

Friction Stir Welding (FSW) is a solid-state joining process involving the frictional heat between the materials and tools. The amount of heat conducted into the workpiece determines the quality of the welded zone. Excessive heat input is the cause of oxides and porosity defects, and insufficient heat input can cause problems, such as tunnel defects. Therefore, analyzing the temperature history and distribution at the center of the Friction Stir Welded zone is very important. In this study, the temperature distribution of the friction stir welding region of an AZ61 magnesium alloy was investigated. To achieve this goal, the temperature and metal flow was predicted using the finite element method. In FE analysis, the welding tool was simplified and the friction condition was optimized. Moreover, the temperature measuring test at the center of the welding region was performed to verify the FE results. In this study, the tool rotation speed was a more dominant factor than the welding speed. In addition, the predicted temperature at the center of the welding region showed good agreement with the measurement results within the error range of 5.4% - 7.7%.

• Journal of Welding and Joining
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• v.28 no.6
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• pp.70-75
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• 2010

This study intends to investigate the weldability and mechanical characteristics of butt weld joints by LAFSW for dissimilar materials (Al6061-T6 and SS400). At optimum welding conditions, the tensile strength of dissimilar materials joints made by FSW is found to be lower than that of LAFSW. Due to the increase in plastic flow and formation of finer recrystallized grains at the TMAZ and SZ by laser preheating in LAFSW, the hardness in LAFSW appeared to be higher than that of FSW. Compared with FSW, finer grain size is observed and elongated grains in parent metal are deformed in the same direction around the nugget zone in TMAZ of Al6061-T6 by LAFSW. Whereas, at weld nugget zone, coarse grain size is appeared in LAFSW compared to FSW, which is owing to more plastic flow due to laser preheating effect. In dissimilar materials joints by LAFSW, ductile mode of fracture is found to occur at Al6061 side with fewer brittle particles. Mixed mode of cleavage area and ductile fracture is observed at SS400 side.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.8
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• pp.706-713
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• 2016

In this study, the welding characteristics of friction stir welding were investigated in accordance with the tool plunge position and cooling to the base materials for the joining of dissimilar materials (A6005-AZ61). Other different welding conditions, such as the tool rotation speed and welding speed, were fixed to 500rpm-30mm/min, respectively, and welding was then carried out by placing the Mg alloy (AZ61) on the advancing side and Al alloy(A6005) on the retreating side. Welding was conducted under six different conditions. To investigate the welding characteristic, tensile test and microstructure observations using an optical microscope were carried out. As the tensile test result, the maximum strength appeared under the condition in which the tool is moved 1 mm to the Mg alloy direction and cooling to the base materials. Under the same welding conditions, the strength with cooling was approximately two times higher than that without cooling. The tool was located in each direction of 1.7 mm from the weld line. Therefore, in the excessive off-set of tool position, the welding integrity was in an extremely poor condition due to the lack of stirring. This study was confirmed by the A6005-AZ61 dissimilar friction stir welding the welding speed and the tool rotation speed. In addition, the temperature control and tool plunge position are important welding parameters.