“…The increase of the weld microhardness under ultrasound could be attributed to the re nement of grain size (in Fig. 10), which corresponded to the study of Chen et al [27].…”
Severe porosity and coarse columnar grain are prone to be formed in the laser-MIG welded joint of aluminum alloy, deteriorating the strength and ductility seriously. In this study, the ultrasound was designed to assist the laser-MIG hybrid welding of aluminum alloy, and the in uence of ultrasonic vibration on weld formation, porosity, and microstructure was investigated. The weld depth was increased from 3.6 mm to 4.2 mm when external ultrasound with the pressure of amplitude transformer (PAT) of 132 N was used, indicating that the penetration ability of hybrid heat sources to the welded plate could be improved. It was attributed to the dispersion effect of ultrasound on arc plasma in the laser channel. The porosity rate was reduced from 5.66-1.05% under PAT of 132 N, because of the increase in escape velocity of bubbles. Moreover, the columnar to equiaxed transformation (CET) of grain in the weld was promoted and the width of columnar grain zone was gradually reduced with the increasing ultrasonic energy, owing to the breaking effect of cavitation and the stirring effect of acoustic stream. As a result, lower porosity rate and ner grain size led to improvement of the microhardness and the strength of weld by ultrasound. The study provides more guidance on employing ultrasound to improve the quality of welded joints.
“…The increase of the weld microhardness under ultrasound could be attributed to the re nement of grain size (in Fig. 10), which corresponded to the study of Chen et al [27].…”
Severe porosity and coarse columnar grain are prone to be formed in the laser-MIG welded joint of aluminum alloy, deteriorating the strength and ductility seriously. In this study, the ultrasound was designed to assist the laser-MIG hybrid welding of aluminum alloy, and the in uence of ultrasonic vibration on weld formation, porosity, and microstructure was investigated. The weld depth was increased from 3.6 mm to 4.2 mm when external ultrasound with the pressure of amplitude transformer (PAT) of 132 N was used, indicating that the penetration ability of hybrid heat sources to the welded plate could be improved. It was attributed to the dispersion effect of ultrasound on arc plasma in the laser channel. The porosity rate was reduced from 5.66-1.05% under PAT of 132 N, because of the increase in escape velocity of bubbles. Moreover, the columnar to equiaxed transformation (CET) of grain in the weld was promoted and the width of columnar grain zone was gradually reduced with the increasing ultrasonic energy, owing to the breaking effect of cavitation and the stirring effect of acoustic stream. As a result, lower porosity rate and ner grain size led to improvement of the microhardness and the strength of weld by ultrasound. The study provides more guidance on employing ultrasound to improve the quality of welded joints.
“…The second way is to apply ultrasound on the filler-wire/probe, which are in contact with the weld pool, so that ultrasound is directly introduced into the weld pool [67, 68]. The third one is to act ultrasound on the arc space to alter the arc/droplet behaviours [69-73]. Figure 13 Schematic diagram of UV-assisted arc welding.…”
Arc welding processes are still widely used in manufacturing industry. To further improve the arc welding efficiency and the joint quality, secondary energy field/source is usually applied to assist the conventional arc welding process. Modelling, sensing and control of such arc welding processes are efficient and powerful ways for process modification and development and complete understanding the underlying interaction mechanism of the auxiliary energy and the welding process. This article reviews the present status in this aspect. A few typical examples such as external magnetic field-assisted gas metal arc welding, ultrasonic vibration-assisted gas tungsten/metal arc welding, and ultrasonic-assisted plasma arc welding are introduced to demonstrate their system, principle and effectiveness. Additionally, some challenges and future outlooks are summarised.
“…Chen et al applied ultrasonic-arc coaxial technology to the welding of Q235 stainless steel, and proved that the texture type was changed and the texture strength was decreased under the action of ultrasound. In addition, the crystal isotropy was improved, and the hardness was increased by about 30 HV [28]. Sun et al applied the ultrasonic-arc coaxial composite technology to TIG (U-TIG), and the experimental results showed that when ultrasonic vibration acted on the arc, the arc thrust was enhanced, and the weld penetration depth was increased by 300% [29].…”
A self-designed ultrasonic-assisted welding platform was built to improve the poor microstructure and properties of conventional TIG welded ferritic stainless steel. The ultrasonic vibration was transmitted to the weld pool through the base metal in the manner of point–surface contact in the optimal position after calculation. The results show that the coarse columnar grains in the welded joint can be transformed into very fine equiaxed grains under ultrasonic vibration, especially the coarse columnar grains near the fusion line where cliff-like refinement occurs. The maximum grain size in the weld seam is reduced from 420 μm to 260 μm, and the average size is reduced by 60%. At the same time, the grain orientation tends to be harmonized. The microhardness of the welded joint is greatly improved on the whole, and the softening of the heat-affected zone caused by grain coarsening is effectively inhibited. Compared with the welded joints without ultrasonic assistance, the tensile strength and yield strength can be increased by 61 MPa and 47 MPa, respectively, under 130 W ultrasonic vibration. By strengthening the weak part of the welded joint, the weldability and toughness reserve of 441 ferritic stainless steel can be significantly improved.
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