• Journal of Welding and Joining
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• v.14 no.6
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• pp.48-57
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• 1996

The weldability of high purity aluminum-lithium binary alloys has been investigated using the Varestraint test. Autogenous GTAW (gas-tungsten-arc-welds) were run along specimens of different lithium concentration using three sets of welding parameters. Welding voltage was held constant at 10 volts. Welding current (70∼100 amps) and travel speed (23∼33 cm/min) were the parameter varied. Hot-tearing susceptibility varied with lithium content and exhibited a steep peak at 2.6 weight percent lithium. Depth of penetration increased with increasing heat input and lithium concentration. The susceptibility is influenced by the wettability of dendrites by the interdendritic eutectic liquid as well as the time available for back-Siting by eutectic liquid. The welding condition of welding current 70A and travel speed 23 cm/min was showed good resistance to cracking in aluminum-lithium alloys. Suggestions for improving weld cracking resistance are also provided.

• Journal of Welding and Joining
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• v.33 no.5
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• pp.31-34
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• 2015

Microstructure and tensile property in the weld heat-affected zone (HAZ) of austenitic Fe-Mn-Al-C low density steels were investigated through transmission electron microscopy analysis and tensile tests. The HAZ samples were prepared using Gleeble simulation with high heat input welding condition of 300 kJ/cm, and the HAZ peak temperature of $1200^{\circ}C$ was determined from differential scanning calorimetry (DSC) test. The strain- stress responses of base steels showed that the addition of V improved the tensile and yield strength by grain refinement and precipitation strengthening. Tensile strength and elongation decreased in the weld HAZ as compared to the base steel, due to grain growth, while V-added steel had a higher HAZ strength as compared than V-free steel.

• Journal of Welding and Joining
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• v.24 no.2
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• pp.57-63
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• 2006

In this study, the curing kinetics and thermal degradation of underfill were investigated using differential scanning calorimetry (DSC) and thermo gravimetry analysis (TGA). The mechanical and thermal properties of underfill were characterized using dynamic mechanical analysis (DMA) and thermo-mechanical analysis (TMA). Also, we presented on underfill dispensing process using Prostar tool. The non-isothermal DSC scans at various heating rates, the exothermic reaction peak became narrower with increasing the heating rate. The thermal degradation of underfill was composed of two processes, which involved chemical reactions between the degrading polymer and oxygen from the air atmosphere. The results of fluidity phenomena were simulated using Star CD program, the fluidity of the underfills with lower viscosity was faster.

• Journal of Welding and Joining
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• v.6 no.2
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• pp.47-55
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• 1988

This paper reports on a study of the influence of welding variables on the weld shape of Al-7020 in pulse-GMA welding. Five variables, i.e., wire feed rate, peak pulse current, welding speed, welding votage, and pulse frequency were investigated for their effects on the weld shape. From the results of the 2$^{n-1}$ fractional factorial design, quantitative effects of each variable and the interaction of two variables were obtained, and consequently wire feed rate, welding voltage, and welding speed were determined as the main welding variables. Supplementary experiment was performed for ivestigating the detailed relationship between the main variables nd the seld shape. In this experiment, the penetation of the seldment increased when the wire feed rate was raised, nad the bead width increased when the welding voltage was raised or the welding speed was reduced.d.

• Journal of Welding and Joining
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• v.16 no.4
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• pp.63-72
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• 1998

In this study, the effects of the current pulsing conditions, on the spatter generation rate during the $CO_2$ gas metal arc welding (GMAW) were investigated. Normally using the inverter type power supply, of which the welding current waveform was regulated to reduce the spatter generation rate, but in this study pulsing was imposed on the welding current. Observation of the metal transfer phenomena during the pulsed current GMAS indicated that the droplet transfer from the electrode via the short circuit transfer and the repelling transfer mode could be minimized by selecting optimum combinations of pulsing parameters, which include base and peak current, base and pak duration. It was also demonstrated in this study that proper combinations of the pulsing parameters led to reduce generation of spatters during GMAW shielded by $CO_2$ gas.

• Journal of Welding and Joining
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• v.17 no.1
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• pp.55-61
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• 1999

The effect of S content in welding wires on the arc stability was investigated, in the region of short circuit transfer and spray transfer. In the region of short circuit transfer, with increasing S content, average arcing time and average short circuit time were decreased. Therefore, droplet transfer frequency was increased, due to the reduction of arcing time and peak current at the moment of arc-reiginition was decreased, due to the decrease of short circuit time. In the region of spray transfer, the fluctuation degree of arc current and arc voltage became more stable, with increasing S content.

• Journal of Welding and Joining
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• v.15 no.6
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• pp.85-95
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• 1997

This study is to investigate the optimum conditions of Nd:YAG laser beam welding for Zircaloy-4 end cap closure by optical fiber transmission. Laser welding parameters which affect the penetration depth and bead width were experimentally examined using the various beam radius by the beam quality analyzer, joint geometries of end cap and the laser parameters which mean pulse width, repetition rate and pulse energy. Also, an optimum welding speed and the effect of assistant gas with varying the flow rate of He were investigated. We found that the laser average power for the end cap welding will be 230W and rotation speed must not exceed 8 RPM, the best position of focus using optical fiber with 600.mu.m will be 2 to 3mm below the surface of the material.

• Journal of Welding and Joining
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• v.20 no.3
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• pp.91-97
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• 2002

Variation of HAZ toughness of Ti-containing steel with nitrogen content was investigated and interpreted in terms of its microstructure and the amount of soluble nitrogen present. The amounts of Ti and Al combined in TiN and AlN, respectively, in HAZ at $1400^{\circ}C$ peak temperature were less than those in base plate; 55~88% in TiN and 21~28% in AlN, indicating the dissolution of nitrifies in HAZ. The calculated amounts of soluble nitrogen using the thermodynamic analysis showed a good agreement with the measured values in other experiment. Therefore, the analysis can be used to estimate the amount of soluble nitrogen in HAZ. Simulated HAZ toughness was influenced not only by its microstructure but also by the amount of soluble nitrogen present after the formation of BN during the cooling cycle of welding. It showed maximum value when the nitrogen content is in stoichiometric ratio with titanium content, showing that soluble nitrogen in HAZ is detrimental to its toughness.

• Proceedings of the KWS Conference
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• 1994.05a
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• pp.44-47
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• 1994

The ageing behavior of Cu-bearing HSLA steels was studied by using Differential scanning calorimetry(DSC), Transmission electron microscopy and hardness tester. Two heat evolution peaks were observed during DSC scans over the temperature range of 25～590$^{\circ}C$ at a heating rate of 5$^{\circ}C$/min. The peaks appeared in low (241∼319$^{\circ}C$ : HSLA-A, 224∼310$^{\circ}C$ : HSLA-B) and high temperature (514∼590$^{\circ}C$ : HSLA-A, 451∼558$^{\circ}C$ : HSLA-B) are attributed to the formation of coherent Cu-clusters and noncoherent $\varepsilon$-Cu phase, respectively. It was confirmed that as ageing proceeds, the coherent bcc Cu-clusters transform to noncoherent fcc $\varepsilon$-Cu phase. In the case of the ageing to peak hardness at 300$^{\circ}C$ and 400$^{\circ}C$, the coherent Cu-clusters contributed to the hardening. As ageing time and temperature increase over peak hardness, noncoherent $\varepsilon$-Cu are formed and hardness decreases.

• Proceedings of the KWS Conference
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• 1994.05a
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• pp.39-43
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• 1994

The effects of ageing treatment on the mechanical properties of two Cu-bearing HSLA(High Strength Low Alloy) steels, HSLA-A and HSLA-B ,were studied by means of SEM, TEM, tensile, charpy impact and hardness tests. These steels showed excellent combination in strength and toughness at an ageing of $650^{\circ}C$ by the precipitation of $\varepsilon$-Cu and low carbon alloying. The peak strength was achieved at an ageing of 50$0^{\circ}C$ in both steels, while the impact energy was very low in this peak strength. With ageing temperature above this temperature, strength was decreased whereas impact energy increased. A marked increase in hardness above 675$^{\circ}C$ was associated with the formation of “M-A constituents” which forms during cooling from austenite-ferrite two phase region. The impact transition temperature of HSLA-A and HSLA-B steels were -l$25^{\circ}C$ and -145$^{\circ}C$, respectively.