• Laser Solutions
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• v.10 no.4
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• pp.1-6
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• 2007

This study includes the effects of shielding gas types and flow rate on Nd:YAG Laser weldability of sintered material. The types of shielding gas were evaluated for He, Ar and N2. Bending strength, porosity rate, hardness and aspect ratio testing of laser weld are carried out to evaluated the weldability. As a results, Ar gas was showed the best welding strength even it has the most porosity content on weld metal, and depend on increases the gas flow rate, it was not only got deeper penetration depth but also showed higher bending strength. Therefore we could know that bending strength is not only affect the porosity content but also melting area.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.2
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• pp.294-301
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• 2012

Shipbuilding industry has used a lot of $CO_2$ gas as a shielding gas for arc welding and thus, development of welding equipment which can reduce the amount of $CO_2$ gas is requested widely. Therefore, this study is focused on the examination of optimum welding torch distance of Tandem welding system as a fundamental study for the optimum shape design of torch nozzle. $CO_2$ shielding gas distribution and welding bead shape formation by the torch distance are examined. Results show that according to the torch distance variation, most effective shielding gas layer can be formed and quantitative determination of the optimum torch distance can result in the reduction of $CO_2$ shielding gas consumption.

• Journal of Welding and Joining
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• v.11 no.1
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• pp.52-61
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• 1993

Laser welding of ASTM no. 1060 Al plate with a pulsed Nd: YAG laser of 200W average power was performed for end capping of KMRR nuclear fuel elements In this research, we performed basic welding experiments. Firstly, laser output parameters which affect laser welding parameters were studied by changing laser input parameters for effective welding of 1060 Al plates. We found that laser power density and pulse energy are important parameters for smooth bead shape. Secondly, welding parameters which affect weld width-to-depth ratio were studied by changing power density and pulse energy, shielding gas, and defocusing. We found that power density must be higher than 0.3 Mw/cm$^{2}$ pulse energy must be higer than 3 J. travel speed must not exceed 200mm/sec, laser focus must be existed beneath 2-3mm from plate surface and helium is proper shielding gas. Thirdly, we studied the weld defects of Al-1060 such as crack and porosity in lap-joint welding. We designed new welding geometry for crack free welding of Al-1060 plates, and obtained crack free weldment but with lack of fusion. However, with Ti, Zr grain refiner elements, we can weld Al plates without solidification hot crack. Finally, we studied the origin of porosity by changing shielding gas. And we found that porosity was resulted from entrapment of shielding gas by the collapsing keyhole.

• Corrosion Science and Technology
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• v.13 no.2
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• pp.70-80
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• 2014

Duplex stainless steels with nearly equal fraction of the ferrite(${\alpha}$) phase and austenite(${\gamma}$) phase have been increasingly used for various applications such as power plants, desalination facilities due to their high resistance to corrosion, good weldability, and excellent mechanical properties. Hyper duplex stainless steel (HDSS) is defined as the future duplex stainless steel with a pitting resistance equivalent (PRE=wt.%Cr+3.3(wt.%Mo+0.5wt.%W)+30wt.%N) of above 50. However, when HDSS is welded with gas tungsten arc (GTA), incorporation of nitrogen in the Ar shielding gas are very important because the volume fraction of ${\alpha}$-phase and ${\gamma}$-phase is changed and harmful secondary phases can be formed in the welded zone. In other words, the balance of corrosion resistance between two phases and reduction of $Cr_2N$ are the key points of this study. The primary results of this study are as follows. The addition of $N_2$ to the Ar shielding gas provides phase balance under weld-cooling conditions and increases the transformation temperature of the ${\alpha}$-phase to ${\gamma}$-phase, increasing the fraction of ${\gamma}$-phase as well as decreasing the precipitation of $Cr_2N$. In the anodic polarization test, the addition of nitrogen gas in the Ar shielding gas improved values of the electrochemical parameters, compared to the Pure Ar. Also, in the erosion-corrosion test, the HDSS welded with shielding gas containing $N_2$ decreased the weight loss, compared to HDSS welded with the Ar pure gas. This result showed the resistance of erosion-corrosion was increased due to increasing the fraction of ${\gamma}$-phase and the stability of passive film according to the addition $N_2$ gas to the Ar shielding gas. As a result, the addition of nitrogen gas to the shielding gas improved the resistance of erosion-corrosion.

• Laser Solutions
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• v.6 no.1
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• pp.25-31
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• 2003

5052 aluminum alloy sheets of 2mm thickness were butt welded using a continuous wave Nd:YAG laser with and without Ar shielding gas. Vickers hardness, transverse-weld tensile and bulge tests were carried out to investigate the effect of Ar shielding gas on the mechanical properties and formability of laser welds. Porosity in the weld metals was investigated using an optical microscope. Mechanical properties and formability of 5052 aluminum alloy laser welds were degraded compared to those of base metal. However, those properties were improved due to the reduced size and number of porosity when Ar shielding gas was used.

• Laser Solutions
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• v.6 no.2
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• pp.19-26
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• 2003

6061 aluminum alloy sheets were I-square butt welded using a continuous wave Nd:YAC laser. Heat inputs were varied from 54.6 to 80 J/mm for butt welding using different sets of the laser power and the weld speed. I-square butt welds were also made with and without Ar shielding gas. The effect of Ar shielding gas and heat input on the mechanical properties and formability was investigated using Vickers hardness, transverse-weld tensile and bulge test. Porosity on the weld beads and sections and hot crack on the fracture surfaces of transverse-weld tensile test specimens were investigated using optical and scanning electron microscopy The experimental results showed that mechanical properties and formability of 6061 aluminum alloy laser welds were degraded compared to those of base metal. Mechanical properties and formability of 6061 aluminum alloy laser welds were not substantially changed when Ar shielding gas was supplied or heat inputs were varied.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.1
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• pp.29-34
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• 2013

The welds tent to be weakened if it is exposed to the air during the welding process. In titanium welding with Gas Tungsten Arc Welding, inappropriate colors of the welds, such as purple/red, blue, yellow, gray, white and pink represents that it is contaminated by oxygen and nitrogen in the air. Shielding gases can be used to protect welds from the contamination. In addition, Weld metal and heat affected zone (HAZ) are also shielded from the air when it is cooled down to the room temperature. In this paper, appropriate shielding gases for the shape and form of Trailing Shielding Jig and torch shielding ($13{\sim}20{\ell}/min$), after shielding ($22{\sim}30{\ell}/min$), and back shielding ($25{\sim}30{\ell}/min$) are studied.

• Corrosion Science and Technology
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• v.16 no.2
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• pp.49-58
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• 2017

Many research efforts on the effect of nitrogen on the corrosion resistance of stainless steels have been reported, but little research has been conducted on the effect of nitrogen for the weldment of stainless steels by the seal-weld method. Therefore, this work focused on the determining the corrosion resistance of tube/tube sheet mock-up specimen for sea water condensers, and elucidating the effect of shielding nitrogen gas on its resistance. The pitting corrosion of autogenously welded specimen propagated preferentially along the dendritic structure. Regardless of the percent of shielding nitrogen gas, the analyzed nitrogen contents were very much lower than that of the bulk specimen. This can be arisen because the nitrogen in shielding gas may partly dissolve into the weldment, but simultaneously during the welding process, nitrogen in the alloy may escape into the atmosphere. However, the pitting resistance equivalent number (PREN) of the interdendrite area was higher than that of the dendrite arm, regardless of the shielding gas percent; and the PREN of the interdendrite area was higher than that of the base metal; the PREN of the dendrite arm was lower than that of the base metal because of the formation of (Cr, Mo) rich phases by welding.

• Journal of Welding and Joining
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• v.17 no.6
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• pp.38-45
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• 1999

Shielding gas has significant effects on arc stability, metal transfer and weld quality in the gas metal arc welding (GMAW) process. The double gas-shielded MAG(DMAG) and auxiliary gas-shielded MAG (AMAG) torches are investigated for their capability to provide argon-rich gas mixture using small amount of argon gas through the inner and auxiliary nozzles, respectively. Argon composition with the DMAG torch is calculated numerically, and compared with the measured data using the gas chromatogrphy. Gas flow pattern of the DMAG torch is calculated to change from the laminar to turbulent flow when total gas flow rate becomes larger than 4.5 liter/min at room temperature. While argon-rich shielding gas was obtained using both the AMAG and DMAG torches, the AMAG torch provides higher argon composition than the DMAG torch, which demonstrates that argon gas can be utilized more efficiently with the AMAG torch.

• Proceedings of the KWS Conference
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• 2006.10a
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• pp.63-65
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• 2006

The paper deals with the effect of hydrogen or helium in argon as a shielding gas on GTA welding of austenitic stainless steel. The studies were carried out in GTA(Gas Tungsten Arc) welding with a non-consumable electrode in case with different volume additions of hydrogen or helium to the argon shielding gas, i.e $5%H_2,\;10%H_2$, 30%He and 67%He. The penetration, welding voltage, microstructure and mechanical property were examined. The deepest penetration was obtained from the sample which was welded under shielding gas of $10%H_2$. The studies showed that hydrogen or helium addition to argon changes the static characteristic of the welding arc. The hydrogen or helium addition to argon increases arc power and the quantity of the material melted. The weld metal penetration depth and its width increased with increasing hydrogen or helium content. Additionally, welding voltage increased with increasing hydrogen or helium content.