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It is of great significance in the field of engineering to repair the surface defects of ZM6 cast magnesium alloy by an arc welding method. Compared with the traditional tungsten inert gas (TIG) welding repair technology, cold metal transfer (CMT) welding repair has the advantages of low heat input, small repair deformation, and high efficiency. It is of great research value to repair the surface defects of ZM6 cast magnesium alloy by CMT welding. In this paper, the effect of CMT welding repair parameters on defect repair forming is systematically studied, and a repair process window free of unfused defects is obtained. The effects of preheating temperature of base material, wire-feeding speed, welding speed, stick-out length of welding wire and shielding gas flow on the spread of magnesium alloy melt and weld formation were investigated by a surface surfacing method. During the welding process, a camera was used to capture images of the arc and droplet features. A pit defect with a depth of 11.5 mm was machined on the surface of the casting, and the effect of five different repair paths on the formation of the repair area was studied. In order to make the repair area have better fusion, reasonable repair parameters are as follows: The preheating temperature range is 310–450 °C, the wire-feeding speed range is 5–7 m/min, the welding speed range is 8–10 mm/s, the stick-out length of the welding wire is 12 mm, the shielding gas flow rate is 20 L/min, and the repair path adopts a continuous linear reciprocating welding path. This study has important significance for guiding the development of CMT repair technology of cast magnesium alloy. [ABSTRACT FROM AUTHOR]

K-TIG welding is an exceptionally efficient welding technique that enables full penetration with a single pass, without the need for groove preparation or wire filling. Comprehending the distinct arc characteristics of K-TIG welding is crucial for exploring the metallurgical process, heat, and mass transfer, and serves as a guide for design considerations. In this study, 2D numerical models of arc plasma in K-TIG welding were established. The arc characteristics of the keyhole and non-penetrated states were compared, while the influence of welding parameters on arc characteristics was further investigated. Finally, the calculated arc pressure was validated by experiments. Results show that the electric potential gradient in the arc column decreases once the keyhole is formed. Simultaneously, the temperature increases at the center of the anode surface and decreases on both sides away from the arc center. Higher welding currents and smaller tungsten tip angles will lead to an increase in the temperature and velocity of arc plasma. As the tungsten tip height increases, the arc temperature increases on both sides but decreases in the arc center, and the pressure in the inner wall of the keyhole shrinks. [ABSTRACT FROM AUTHOR]

As a highly efficient thick plate welding resolution, narrow gap gas tungsten arc welding (NG-GTAW) is in the face of a series of problems like inter-layer defects like pores, lack of fusion, inclusion of impurity, and the sensitivity to poor sidewall fusion, which is hard to be repaired after the welding process. This study employs numerical simulation to investigate the molten pool behavior in NG-GTAW root welding. A 3D numerical model was established, where a body-fitted coordinate system was applied to simulate the electromagnetic force, and a bridge transition model was developed to investigate the wire–feed root welding. The simulated results were validated experimentally. Results show that the molten pool behavior is dominated by electromagnetic force when the welding current is relatively high, and the dynamic change of the vortex actually determines the molten pool morphology. For self-fusion welding, there are two symmetric inward vortices in the cross-section and one clockwise vortex in the longitudinal section. With the increasing welding current, the vortices in the cross-section gradually move to the arc center with a decreasing range, while the vortex in the longitudinal section moves backward. With the increasing traveling speed, the vortices in the cross-section move toward the surface of the molten pool with a decreasing range, and the horizontal component of liquid metal velocity changes in the longitudinal section. For wire–feed welding, the filling metal strengthens the downward velocity component; as a result, the vortex formation is blocked in the cross-section and is strengthened in the longitudinal section. [ABSTRACT FROM AUTHOR]

Tungsten inert gas (TIG) is currently one of the most widely applied welding technologies. However, the arc energy divergence and high heat input of conventional TIG can lead to welding defects in heat-input-sensitive alloys (such as Inconel 718). Introducing a fast-frequency pulsed current (≥20 kHz) in TIG creates a welding process named fast-frequency pulsed tungsten inert gas (FFP-TIG). The arc behavior of FFP-TIG has advantages over conventional TIG in terms of arc contraction, arc pressure, and energy density. With an increase in the FFP current amplitude or frequency, the arc diameter and arc area are reduced, the arc pressure at the center of the arc is increased, and the arc energy divergence and arc temperature are reduced. The FFP-TIG weld method was adapted for Inconel 718 based on FFP-TIG arc behavior. This study provides fresh insight into the development and application of FFP-TIG arc physics research and industrial applications. [ABSTRACT FROM AUTHOR]

Narrow gap TIG welding is a high efficiency and low-cost welding technique for heavy structures building. Due to the narrow groove's constriction, the TIG arc characteristics are different from butt welding. Understanding the unique arc characteristics of narrow gap TIG welding is the foundation for investigating the heat and mass transfer, metallurgic process, as well as process design. This research conducted numerical simulation on the TIG arc plasma in the narrow groove. The effects of welding current and arc length on the arc characteristics are investigated. Results show that, with the welding current increasing, the global velocity magnitude of plasma rises. The evolution of axial velocity and radial velocity has different responses to the current changes. The arc pressure increases drastically, and the global temperature of arc plasma also goes up. With the arc length increasing, global axial velocity rises, but the axial velocity and its gradients decrease near the anode surface. Centripetal radial velocity near the cathode increases, while centrifugal radial velocity rises at the outside of arc plasma and drops near the central axis. The maximum arc pressure on the anode surface decreases. At the lower part of the arc, arc temperature decreases near the central axis and increases at the outside of the arc. [ABSTRACT FROM AUTHOR]

The arc physical properties of the plate-butt welding and narrow gap welding were simulated. The narrow gap groove affects the arc properties, and the narrow gap welding arc has its special properties. The shielding gas flows along the longitudinal direction in the narrow gap groove, and the arc temperature field constricts transversely but expands longitudinally. The high-temperature region expands and the welding heat efficiency increases. The current density is larger for narrow gap welding, which induces the larger Lorentz force to accelerate the plasma flow. The axial and radial plasma flow velocities are both larger for narrow gap welding, which leads to the larger arc pressure and shear stress. The results have good agreements with the experiments results. [ABSTRACT FROM AUTHOR]

For short-circuiting transfer, a smaller short-circuiting current is useful to obtain a better quality of welded joints, such as less spatter and better welding surface. By analyzing images from the high-speed camera, welding electrical signal, and current-voltage (U-I) cycle diagram, stable welding process could be obtained by adding pulsed ultrasonic into the arc. The ultrasonic radiator height, as one of the most important parameters, could affect the energy of acoustics field in pulsed ultrasonic-assisted gas metal arc welding. According to droplet transfer frequency, short-circuiting current and U–I cycle diagram, the ultrasonic radiator height was optimized and the optional ultrasonic radiator height was determined to be 12 mm. The sound radiation force was the main reason for the reducing short-circuit transfer cycle. [ABSTRACT FROM AUTHOR]

In narrow gap gas metal arc welding (GMAW), it is useful to understand the arc behaviors to ensure the weld quality. Arc behaviors are strongly affected by the shielding gas composition. In this study, a three-component shielding gas mixture was used in tandem narrow gap pulsed GMAW, and the effect of its composition on arc behaviors and weld formation were investigated. The shielding gas included argon, carbon dioxide, and helium. The arc behaviors and electrical characteristics were recorded by a high-speed camera and an electrical signal acquisition system. The results show that the arc behaviors in different shielding gas are different. The arc expands and the arc length decreases with the increase of CO content or helium content. The arc is the widest when the shielding gas is 80%Ar10%CO10%He. The weld shape was observed, and it was found that the weld width increases first and then decreases with increasing of the CO content. When the helium content is below 15%, the weld width increases as the helium content increases, but when the helium is 15%, the weld width drops due to the decrease of arc length. When the helium content is above 15%, the weld width continues to increase as the helium content increases. The largest weld width can be obtained in 80%Ar10%CO10%He. [ABSTRACT FROM AUTHOR]

At constant current, the arc voltage increases with increasing helium or CO 2 content. At constant wire feed speed and constant voltage, as the helium or CO 2 content increases, the welding current decreases. The arc length decreases significantly with the increase of CO 2 content and arc core expands with the increase of helium content. When the shielding gas composition changes, arc properties and wire melting characteristics both change and the arc works at a new equilibrium point to keep the wire melting rate equal to wire feed speed. Shielding gas with the addition of helium presents a bowl weld bead profile. The depth of sidewall fusion increases as helium content increases. The welding process and weld quality are good when the shielding gas is 80%Ar10%CO 2 10%He. [ABSTRACT FROM AUTHOR]

Tungsten inert gas (TIG) arc welding of 2219 aluminum alloy was assisted with a trailing periodic ultrasonic vibration, which was output from a trailing roller behind the welding torch. It was found that the weld appearance was periodically convex due to the periodic input of ultrasonic vibration. With the addition of ultrasonic vibration, the columnar grains in the weld zone transformed to equiaxed grains, so along the longitudinal direction, the equiaxed grains and the columnar grains were alternately distributed due to the periodic ultrasonic vibration. The effects of different ultrasonic powers were investigated. The penetration depth and the amount of the melting metal both increased as the ultrasonic power increased. The coarse precipitated phases in the weld zone tended to disperse uniformly under ultrasonic vibration. Compared with conventional TIG welded joints, the hardness of the weld zone of the ultrasonic assisted TIG welding increased by 8.43%, and the tensile strength increased by 29.02%. The ultrasonic cavitation could decrease the nucleation radius and break the dendrites, which led to the grains' refinement and the final mechanical properties' improvement. [ABSTRACT FROM AUTHOR]

• Non-axial symmetric arc characteristics in narrow gap TIG welding were simulated and validated experimentally. • Both arc weaving and anode surface shape changes influence the temperature distribution and heat efficiency of TIG arc significantly. • Arc weaving makes the arc pressure deviate from Gaussian distribution while anode surface changes have limited effect. Narrow gap TIG welding is a high-quality solution for joining thick structures with reduced costs. However, the matching between numerous parameters is required to achieve satisfactory weld quality since its nature of multi-layer and single pass welding makes the repair difficult. This study aims to lay the theoretical foundation for the process design by building a deep understanding of the arc characteristics during narrow gap TIG welding. The 3D MHD simulation is carried out to investigate the influence of arc weaving and anode surface shape on characteristics of steady arc plasma, and the results are validated by experiments. Results show that as the electrode weaves from groove center to the side wall, local concentration of current density leads to the climbing of arc root on the side wall. The flow pattern of arc plasma changes from reverse circulation to inclined downward, results in the decrease of heat efficiency. As the shape of anode surface changes from concave downward to convex upward, the arc root shrinks but with a decrease of heat efficiency. [ABSTRACT FROM AUTHOR]