The effects of welding conditions on the residual stress and distortion behaviors of the full and partial-penetration weld joints with thin steel plates in the use of the electron beam welding process have been studied. Residual stresses and angular distortion were measured, and the experimental results have been verified with the aid of the thermal elastic-plastic analysis by the finite element method. The experimental results of residual stress and angular distortion have been clarified to be similar to the analysis results. The residual stresses ( T and L ) in the transverse and longitudinal directions with respect to the weld line have been confirmed to be shifted to the compression side in the vicinity of the weld toe when the beam power was higher and the beam diameter was smaller. The magnitude of residual stresses at the weld toe has been found to be related to the penetration depth. It has also been revealed that angular distortion tends to increase as the beam power becomes higher.

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The behavior of cathode spots in stationary argon alternating current tungsten inert gas welding of aluminum was clarified in this study. The temporal variation in cathode spot distribution during electrode positive (EP) polarity was, for the first time, revealed quantitatively based on high-speed video camera observation with a frame rate of 500 000 fps. In addition, the weld pool surface temperature at the start and end of EP polarity was also measured using the two-wavelength temperature measurement method to clarify the relationship with the cathode spot behavior. As a result, the general tendency of the life cycle of the cathode spot was clarified. The first cathode spot appeared and divided outside the weld pool. Following this, they moved rapidly toward the weld pool center within 100 µs. After that, the cathode spot group became an uneven and ringshaped distribution, which expanded outward with time with a velocity of approximately 1 m s −1 . The cathode spots have a random movement with the average velocities of each cathode spot on the liquid and solid surface being about 142 ± 59 m s −1 and 87 ± 44 m s −1 , respectively. The ratio of the number of cathode spots located in the weld pool to the total number of cathode spots decreased from 100% to 37.4% with elapsed time, except right at the beginning. Furthermore, the temperature of the center surface of the weld pool was 1400 K, and this gradually increased to a slightly higher temperature than the melting point of aluminum around the weld pool boundary at the start of EP polarity. The maximum temperature at the center is considered to be linked with absence of a cathode spot. The temperature at the center decreased by 150 K at the end of EP polarity due to the temporal expansion in the ring-shaped distribution of the cathode spot group leading to a decrease in heat input around the center.

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The paper evaluates the performance of alternating current (AC) square waveform submerged arc welding (SAW) as a candidate technology for manufacturing thick welds for high-pressure vessels. A new mathematical formulation for calculating melting efficiency in square waveform arc welding is presented. The melting efficiency and the heat consumption are presented as a mathematical model of welding parameters, namely welding current, welding speed, current frequency, and electrode negativity (EN) ratio. The proposed approach is demonstrated through the welding of 2.25Cr-1Mo heat-resistant steel performed over a wide range of welding parameters. The investigation provides deeper insights into the interplay between process parameter, total heat consumption, and melting efficiency. The effect on flux consumption is also explained. The melting efficiency is inversely proportional to flux consumption. The welding heat does not necessarily promote the plate melting. Improper use of welding heat may lead to decreased melting efficiency and increased unwanted melting and consumption of welding flux. Compared to the conventional direct current (DC) power sources, the AC square waveform welding achieves almost the same order of melting efficiency with added advantages of better weld bead shape and flux consumption in a desirable range. The two additional parameters (frequency and EN ratio) of the AC square waveform power source provide more freedom to fine-tune the process and thereby efficiently use welding heat. The results of this investigation will be advantageous to the designers and fabricators of high-pressure vessels using AC square waveform welding.