• Journal of Welding and Joining
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• v.10 no.1
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• pp.20-34
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• 1992

Characteristics of two correcting methods, a new Autogeneous GTAW heating (TIG) method and the conventional GMAW bead-on plate welding(MIG) method, for distorted aluminum fabrication structures were studied. As a result of microscopic study of Autogeneous GTAW heating and GMAW bead-on plate welding areas, porosities in weld metal and surface cracks in local heating zone were found. Through the mechanical tests, it was verified that porosities decrease tensile strength and surface of distortion, angular displacement and transeverse shrinkage were measures and compared. In order to investigate changes of material properties in heating area and cause of defects such thermal stresses were calculated by ADINA. Through the computations of transient thermal stresses and microscopic observation of fracture surface, thermal stress was found to be the cause of crack during Autogeneous GTAW heating.

• Journal of Welding and Joining
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• v.21 no.5
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• pp.540-546
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• 2003

Recently Al alloys are being used gradually for structural materials of transports. In welding of Al alloys used for transports, good weldabilities as well as adequate mechanical properties of the welds should be ensured as structural materials. In this study, the welds formation, macro and microstructural characteristics, generation of defects and hardness distribution in welds of Al alloys of 5083, 6N01 and 7N01 by DCSP- and AC-GTA welding process, were investigated. The deeper penetration was obtained in all welds of the alloys by DCSP-GTAW with He gas, compared with those by using AC-GTAW. The 6N01 alloy showed high susceptibilities to solidification cracking in weld metal and liquation cracking in HAZ of the welding beads of both DCSP- and AC-GTAW process. The cracking ratio of 6N01 alloy was increased with increasing of welding current. The porosity ratios in weld metal of all alloys used were extremely low including all welding conditions of DCSP-GTAW. However, in AC-GTAW process, the porosity ratios of the welds using Ar gas showed much higher values than those using He gas.

• Journal of Welding and Joining
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• v.12 no.4
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• pp.41-49
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• 1994

This study is to compare the welding quality of API 5L-X65 Steel- pipe's for natural gas transmission piping applied by SAW at shop and by GTAW-SMAW at site. The results can be summarized as follows; 1) Tensile strength of the welded zone by SAW(611.5 MPa) and by GTAW-SMAW(608.6 MPa) was maintained greater than that of the base metal(583.5 MPa). 2) Hardness of the welded zone and HAZ by SAW(Hv 194.8) & GTAW-SMAW (Hv 196.1) was slightly increased above that of the base metal (Hv 168.8), but less than the maximum allowable hardness(Hv 248). 3) Impact value of the welded zone by SAW(126.8 J) & GTAW-SMAW(88 J) became lower than that of the base metal(282.5 J), but was above the requirement of API 5L(68J). 4) Microscopic structure of the welded zone and HAZ by both SAW & GTAW-SMAW became fine-grained.

• Proceedings of the KWS Conference
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• 2004.05a
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• pp.182-184
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• 2004

GTAW of titanium using flux cored wire was exploited. Flux cored wire with MgF$_2$ resulted in 60% deeper penetration than conventional active GTAW which applys fluxes in the form of paste. Emission spectroscopy of the arc with MgF$_2$ showed Ti II peak, indicating higher temperature arc. Elux cored wire formed weld metal with reasonably low oxygen content.

• Journal of Welding and Joining
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• v.32 no.6
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• pp.47-55
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• 2014

The purpose of the study is to produce a mechanically improved weld and minimum variation of color through comparing unpulsed and pulsed GTAW (Gas Tungsten Arc Welding) for pure titanium (CP grade7) tube. Pulsed GTAW using 60 A peak current and 20 A background current (1:9) achieved the wider window of welding conditions having part and full penetration without burn-through than the case of unpulsed GTAW. Moreover, the pulsed welding reduced a discoloration on the back bead of the weld and the size of microstructures (basket weave and serrated ${\alpha}$). That is because the pulsed welding has it's a low heat input and severe weld flow induced from electric current variation. Furthermore, the pulsed welding improved the bending property of the welded Ti tube. The enhanced bending property for the pulsed GTAW was due to the insignificant discoloration on the weld surface with maintaining the metal polish.

• Proceedings of the KWS Conference
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• v.43
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• pp.135-137
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• 2004

• Proceedings of the KWS Conference
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• 1995.10a
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• pp.70-74
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• 1995

• Proceedings of the KWS Conference
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• 2000.10a
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• pp.61-62
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• 2000

• Journal of Welding and Joining
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• v.33 no.5
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• pp.14-19
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• 2015

This study has been performed to investigate the adhesive slag at GTAW weld zone after FCAW multi-pass welding. The cause of adhesive slag formation was examined using optical microscope, field emission scanning electron microscope(FE-SEM) and XRD analysis. The results obtained in this experiment are summarized as follows. Slag of GTAW weld zone surface during welding were formed by mixing the presence of slag in FCAW weld zone. While the slag cools, Cr-spinel phase were formed due to reactions in slag/metal interface. Also, a Cr moves form the weld metal to the slag to strong affinity between oxide atoms and Cr atoms. Hence, detachability of slag was exacerbated by decreasing the interfacial tensions between slag and weld metal.

• Journal of Welding and Joining
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• v.20 no.4
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• pp.517-524
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• 2002

An overlaying of the seating surfaces of engine valves by OAW, GTAW or PTA weldings are common practice. The OAW method of a lower torch energy density compared to GTAW and PTA methods produces smoother deposits but the pain size at the vicinity of the interface is increased remarkably up to $30~50{\mu\textrm{m}}$ (that of base metal is about $10\mu\textrm{m}$). It's grain coarsening and the solute dilution are related to the decarburizing during OAW could be minimized by reducing the preheating temperature and by maintaining the carbide precipitates in base metal prior to welding. The formation of columnar structures and carbide precipitation zone in the vicinity of the GTAW welded interface, because of the high heat concentration, causes weakened zone on the valve seat face. The width of the reaction boundary zone is about $50\mu\textrm{m}$ for PTA and GTAW overlaying, and about $150\mu\textrm{m}$ for OAW welding. The smaller width of the reaction boundary zone is the less the solute-dilution rate. Thereby PTA welding may be recommended for overlaying of the seating surfaces.