Arc Oscillation Research Articles

Dendrite remelting during arc oscillation welding of magnesium alloys: a phase-field study

Dendrite remelting during arc oscillation welding of magnesium alloys: a phase-field study

Tailoring the surface finish, dendritic microstructure and mechanical properties of wire arc additively manufactured Hastelloy C276 alloy by magnetic arc oscillation

In this study, magnetic arc oscillation (MAO) at three different frequencies (5 Hz, 10 Hz and 20 Hz) was applied during deposition of a Ni-base alloy, Hastelloy C276, by wire arc additive manufacturing (WAAM). The microstructure, surface finish and the mechanical properties of WAAM deposited Hastelloy C276 alloy samples with MAO were investigated and compared with the counterpart without the application of MAO. On-line monitoring of the arc movement and molten pool morphologies showed that the incorporation of MAO during WAAM may reduce the arc density during deposition, leading to a decrease in the solidification time. This, in turn, improved the surface accuracy of the as-built alloys. Furthermore, through the application of MAO, the dendrites exhibited a higher variety of growth orientations, and reduced dendrite arm spacings (DAS). The MAO at 5 Hz appeared to enhance the mechanical properties of the produced alloy, while the application at the higher frequencies of 10 Hz and 20 Hz led to less pronounced effects on the mechanical performance improvement. This study enhanced our understanding of the correlation of MAO processing-dendritic microstructure development-mechanical property for the Hastelloy C276 alloy prepared by WAAM, providing guidelines for the utilization of the MAO approach for tailoring the microstructure and the mechanical properties of WAAM produced alloys.

Manipulating heat density to enhance the performance of Aluminium Alloy-Steel joints using arc oscillations in the GTAW process

The present study shows the effect of arc oscillations in improving the mechanical properties of Steel/Aluminium lap joints in the GTAW process. Arc oscillations produce the weaving pattern to manipulate the heat energy density on the base metal. Fe-Al joints were prepared with different heat inputs by varying the welding current and welding speed. The thermal profile and the intermetallic compound layer results indicate the decrease in heat energy density with arc oscillations. Further, the mechanical properties of the joints were compared with no weaving condition and found the enhancement in aesthetics, microhardness, and failure strength of the Fe-Al joints with arc oscillations.

Low current arc ignition stability in micro-TIG welding

Micro‑tungsten inert gas (TIG) welding is widely used in electronic component manufacturing. Arc ignition under low current should be employed to avoid burning the micro-component. However, it is relatively complex to manipulate. To improve the stability and reliability of the arc ignition under low current, the effect of the ignition method, cathode spot motion (CSM), and welding circuit inductance is investigated. High voltage arc ignition (HVAI) experiments are carried out with different inductances under various CSM amplitudes. A high-speed digital camera is employed to record the arc image, while a digital oscilloscope is used to simultaneously detect the arc voltage and current waveforms. The results show that HVAI can achieve smooth arc ignition with the low current in a relatively long discharge gap. The inductance in the welding circuit plays an effective role in maintaining the burning of the micro-arc. However, overly high inductance prevents arc formation just after the breakdown of the gap. When a traditional TIG welding torch is used, cathode spots move violently at the beginning of the low current arc ignition. This results in arc oscillation in the space or even rapid extinguishing. By placing an insulating ceramic tube on the tungsten electrode, the emission of electrons can be limited to the electrode tip. This, in turn, restricts the range of motion of the cathode spots to the tip region. Consequently, low-current arc ignition performance is improved.

Appreciable-tuned ferrite/austenite phase balance in the fusion zone of GTAW welds via an assisted magnetic field

In the present paper, a transverse magnetic field was applied to gas tungsten arc welding (GTAW) for 2205 DSS in order to regulate the weld microstructure, which has not been investigated so far. The results indicated that the application of magnetic field not only can increase the austenite/ferrite phase ratio of the welds, but also refine the ferrite grains, and a magnetic field with a frequency of 1 Hz worked best. Both of the above can be attributed to the slower cooling rate of the welding pool with arc oscillation. Hardness test showed that the arc oscillation exerted a significant influence on hardness distribution. Under the effect of a low frequency (1 Hz) magnetic field, the hardness level of the weld metal was close to that of the base material. However, when no magnetic field was applied, the hardness level of the weld increased.

The Influence of Magnetic Arc Oscillation on the Deposition Width Variation along the Length of Multi-layer Single-Pass Walls Produced by Wire Arc Additive Manufacturing Process

In this work, a wall printer system was developed, and multi-layer single-pass walls of low carbon steel were produced by the Gas Tungsten Arc Welding-based Wire Arc Additive Manufacturing process with and without Magnetic Arc Oscillation. The influence of the longitudinal oscillating movement of the welding arc during the layer deposition process on the wall geometry was evaluated using cross-sectional macrographs from samples removed from the arc striking point, arc extinguishing point, and middle of the wall. The results show that the wall becomes thinner, and the width variation along the wall length decreases when Magnetic Arc Oscillation is applied. The weld penetration also becomes less deep. A physical model based on the arc force and the magnetic force that acts on the weld pool during layer deposition was proposed to explain the influence of Magnetic Arc oscillation on the width variation noted along the wall length. Because of the alternating movement of the welding arc, the plasma jet and molten metal flow change the direction continuously. As a result, the molten metal does not concentrate at the beginning or end of the deposition length, and the width variation problem is minimized.

Wetting behavior of melt and its effect on lack of fusion in arc oscillating NG-GTAW

• A novel single-sidewall wetting test is developed to study the wetting behavior of melt on the sidewall. • Arc oscillation can promote the wetting behavior of melt. • The effect of arc force and surface tension on the wettability of melt is first established in arc oscillating NG-GTAW. • Excellent wetting of melt on the sidewall contributes to the elimination of lack of fusion. The wetting test is first used to study the effect of oscillating arc on the melt flow. A novel wetting method, single-sidewall wetting test, is developed to study the wetting behavior of melt on the narrow gap sidewall and its effect on lack-of-fusion defects is also discussed in arc oscillating NG-GTAW (narrow gap gas tungsten arc welding).The results show that the arc oscillation contributes to the improved wetting of melt on the plate and narrow gap sidewall. In the plate wetting test, variation of surface tension caused by heat input is crucial for wettability, while in the narrow gap, the improvement of wettability is attributed to the interaction of arc shear force, arc pressure and surface tension. As the increase of magnetic flux density, the wettability of melt on the sidewall in narrow gap gradually becomes better. However, the monotonic increasing trend of wettability with respect to the magnetic flux density does not always hold. When the best wettability is obtained, the melt surface is also more even, both of which can contribute to good fusion in the narrow gap. The welded joint without lack-of-fusion defect is obtained by using the magnetic field parameter covered with the best wettability of the melt on the sidewall.

Numerical investigation of heat flux distribution on the welding groove face in magnetic oscillation arc narrow gap GTAW

Obtaining uniform penetration on welding groove faces is one urgent problem in oscillation arc narrow gap welding; however, the heat flux distribution on the groove face under the deflected welding arc is difficult to investigate by the experimental method. In this article, a unified three-dimensional model is developed to study the heat flux distribution on groove faces. The model includes the electrode, welding arc, workpiece, and their coupling. The plasma arc profile, heat flux characteristics, and weld pool formation were simulated. Based on the simulation results, the following conclusions were contained. The deflecting degree of the welding arc axis is increased with the increasing of extra magnetic-field intensity, and this leads to the change of the distribution of conduction heat flux and electric heat flux. At the groove bottom, both heat fluxes move to one side, and their distribution shape changes from circular to elliptical. At the sidewall, the distribution shape of conduction heat flux is triangular, and that of electrical heat flux is elliptical. The maximum value of heat flux density decreased, and the affected area was increased with the associate of the extra magnetic field. The simulation welding bead was in agreement with the experimental result.

Numerical Analysis of the Heating Characteristics of Magnetic Oscillation Arc and the Fluid Flow in Molten Pool in Narrow Gap Gas Tungsten Arc Welding

Magnetic oscillation arc (MOA) technology was developed to avoid insufficient fusion defects appearing at the sidewalls in narrow gap gas tungsten arc welding (NG-GTAW). In this work, a unified model was developed to simulate the process of MOA assisted NG-GTAW. The model included the MOA, welding pool, workpiece and the coupling interaction between them. The heating characteristic of the MOA and the flow of liquid metal were simulated, and the mechanism of forming a uniform welding bead under MOA was investigated. It was found that if the magnetic flux density increased to 9 mT, the MOA could point to the sidewall directly; the maximum heat flux at the bottom declined by almost half and at the side, it increased by more than ten times. Additionally, the heat flux was no longer concentrated but dispersed along the narrow groove face. Under the effect of MOA, there were mainly two flow vortexes in the molten pool, which could further increase the heat distribution between the bottom, sidewall and corner, and was beneficial for the formation of a good-shape weld. The model was validated by experimental data.

Influence of the Longitudinal Magnetic Field on the Formation of the Bead in Narrow Gap Gas Tungsten Arc Welding

The oscillation arc assisted by an extra alternating longitudinal magnetic field (LMF) in narrow gap tungsten arc welding is proved to be effective in avoiding welding defects due to insufficient fusion at the side walls in joining thick wall plates. The behavior of the welding arc and molten pool under the LMF is simulated to reveal the influence of the LMF on the formation of a uniform penetration weld bead. A unified mathematical model was developed for the narrow gap tungsten arc welding including the plasma arc, molten pool, electrode, and their interactions. Under the LMF, the whole welding arc is deflected and oscillates between the two side walls. When the magnetic-field strength is larger than 6 mT, the axis of the arc deflects to the side wall; the maximum value of heat flux at the bottom decreases by one-half, and the maximum value at the side wall is increased by a factor of ten. On the other hand, under the LMF, the forces acting on the molten pool are changed; the fluid flow pattern is helpful to increase the heat transferred to the side walls. The model is validated by experimental results. Both the percentage deviations of the simulation weld penetration at the side wall and at the bottom from the experimental results are lower than 10%.

Effects of the welding current on the mechanical and metallurgical properties of a magnetic oscillated arc welded AZ31B magnesium alloy

Abstract In this study, the effect of current on the tensile and microstructural characteristics of magnetic arc oscillation welded AZ31B magnesium alloy joints has been investigated. Five joints were constructed using different levels of current (65 A - 85 A). It was found that the joints constructed using a current of 75 A yielded superior tensile properties as compared to the other joints. The formation of finer grains and higher hardness in fusion zone and uniformly distributed precipitates are the main reasons for the superior tensile properties of these joints.

Chronology of the marine terraces of the Crotone Peninsula (Calabria, southern Italy) by means of infrared-stimulated luminescence (IRSL)

The Crotone Peninsula (southern Italy) preserves a well developed flight of marine terraces generated by the interplay of uplift of the Calabrian arc and late Quaternary eustatic oscillations. Good chronologic control on the formation of these raised geomorphic features would help constrain regional tectonic and stratigraphic models. However, precise age assignment and correlation of the individual terraces is hampered by lack of material suitable for radiometric dating.With the goal of improving the resolution of the chronology of the terraces, nine samples were collected from four stratigraphically distinct terraced units and dated with the infrared-stimulated luminescence (IRSL) technique applied on feldspar grains. The obtained ages are consistent with the stratigraphic arrangement of the terraces, with samples from higher terraces older or overlapping in age with those from lower terraces. Three samples from the highest (Cutro) terrace indicated a minimum age ≥ MIS (Marine Isotope Stage) 7. Two samples from the second of the four examined terraces, which is generally correlated with MIS 5.3, gave ages that correlate instead with MIS 5.5 and 5.1, revealing more internal complexity and tectonic disruption than previously inferred from this terrace. Luminescence dating was applied for the first time to the deposits of the Capo Colonna terrace, with results indicating a MIS 5.1 age. Finally, one sample from the lowermost (Le Castella) terrace confirmed the preservation of raised marine deposits from MIS 3, a relatively uncommon finding for the Mediterranean region.These results highlight how IRSL dating can contribute to the development and refinement of a chronostratigraphic context for a flight of marine terraces and, ultimately, to a clearer understanding of the combined tectonic and eustatic controls affecting the morphodynamic evolution of a marine coastal sector. More specifically, they confirm the persistence of relatively high average uplift rates (on the order of 1 mm/yr) over the last two glacial cycles in the Crotone Peninsula and the important role of a local component of tectonic and deformative displacement superimposed on the regional uplift.

Effect of transverse arc oscillation on morphology, dilution and microstructural aspects of weld beads produced with short-circuiting transfer in GMAW

This work investigates the effects of transverse arc oscillation in gas metal arc welding (GMAW) with metal transfer by short circuit using the AISI 316L alloy as the base metal. For this purpose, the influence of the oscillation frequency (f) and the wire-feed speed (Va) at three levels was analyzed, keeping a constant triangular weaving pattern and a fixed welding speed. The results show that an increase in oscillation frequency leads to an increase in the resulting welding speed, resulting in lower welding energy. Regarding weld bead morphology, the transverse arc oscillation reduced the reinforcement, the wetting angle, the penetration and the convexity index (CI < 30%). On the other hand, higher dilution values were obtained. Finally, a clear microstructure refinement tendency became evident when applying the weaving technique.

Effects of the welding current on the mechanical and metallurgical properties of a magnetic oscillated arc welded AZ31B magnesium alloy

Abstract In this study, the effect of current on the tensile and microstructural characteristics of magnetic arc oscillation welded AZ31B magnesium alloy joints has been investigated. Five joints were constructed using different levels of current (65 A - 85 A). It was found that the joints constructed using a current of 75 A yielded superior tensile properties as compared to the other joints. The formation of finer grains and higher hardness in fusion zone and uniformly distributed precipitates are the main reasons for the superior tensile properties of these joints.

Modification of droplet morphology and arc oscillation by magnetic field in laser-MIG hybrid welding

In this paper, we presented the morphological characteristics of droplet and arc during alternating magnetic field assisted laser-MIG welding. High speed camera was used to map the effect of magnetic intensity and frequency on droplet transfer and arc shape. Results revealed that the magnetic field indeed modified droplet morphologies and hence pointing direction. This appearance was mainly attributed to the centrifugal force during droplet spinning and resultantly reduced effective potential energy (mechanism I). Moreover, combined effect of laser and magnetic field induced a regularly altered axial asymmetry of arc along the welding direction. Cause of this arc oscillation was due to “particle packing effect” in one side during laser-MIG welding (mechanism II). At last, the optimum magnetic field parameters during the laser-MIG parameters (2000 W, 150A and 1.1 m/min) was concluded as B(mT)f(Hz)≤0.8 and f(Hz)>12t0.

Effect of Magnetic Arc Oscillation on the geometry of single-pass multi-layer walls and the process stability in wire and arc additive manufacturing

Abstract Magnetic Arc Oscillation was applied during the construction of single-pass multi-layer walls of low carbon steel and Ti6Al4V by the Gas Tungsten Arc Welding-based Wire and Arc Additive Manufacturing process, and the influence on the geometry and the process stability was evaluated. The geometric features were assessed using transverse section macrographs and the effects of different patterns and frequencies of oscillation on the arc characteristics, metal transfer and weld pool behavior during the layer deposition were investigated using high speed and welding cameras. The results show that this technique is efficient for making thinner walls by minimizing the overflow of the weld pool and, in some conditions, increasing deposition efficiency. Furthermore, the distribution of material along the wall length becomes more homogeneous. An explanation of the effects of Magnetic Arc Oscillation on the wall geometry based on forces that act on the molten metal during layer deposition was made. Because of the swinging movement of the welding arc, the heat is distributed over a larger area, and the power density decreases. Thus, fewer previous layers are remelted, and the volume and the weight of the weld pool reduce. The weld pool temperature drops, and the surface tension force and the viscous friction increase. The distribution of arc pressure also becomes less concentrated, and the arc force on the molten metal decreases. Additionally, a magnetic force appears on the molten metal, which contributes to a change in the direction of the resultant force on the weld pool.

COMPARISON STUDY OF CONSTANT CURRENT AND ARC OSCILLATION TECHNIQUES ON GTA WELDED AZ31B MAGNESIUM ALLOY JOINTS

The challenges of achieving significant weight reduction in the automobile industry in the context of fuel savings, recyclability and emission reduction has promoted focus on lightweight metals such as magnesium. GTA welding technology is the main welding method adopted for magnesium alloys because of its advantages of utility and economy. Both magnetic arc oscillation and current pulsing techniques resulted in significant microstructural refinement in weld fusion zone. Hence in this investigation an attempt has been made to study the constant current and arc oscillation on tensile and microstructural characteristics of gas tungsten arc welded AZ31B magnesium alloy joints. From this investigation, it is found that the joints fabricated with magnetic arc oscillation having the superior tensile properties compared to constant current welding. The formation of fine grains and higher hardness in fusion zone are the main reasons for the superior tensile properties of these joints.

COMPARISON STUDY ON PULSED AND ARC OSCILLATION TECHNIQUES OF GTA WELDED AZ31B MAGNESIUM ALLOY JOINTS

The challenges of achieving significant weight reduction in the automobile industry in the context of fuel savings, recyclability and emission reduction has promoted focus on lightweight metals such as magnesium. GTA welding technology is the main welding method adopted for magnesium alloys because of its advantages of utility and economy. Both magnetic arc oscillation and current pulsing techniques resulted in significant microstructural refinement in weld fusion zone. Hence in this investigation an attempt has been made to study the arc pulsing and arc oscillation on tensile and microstructural characteristics of pulsed current gas tungsten arc welded AZ31B magnesium alloy joints. From this investigation, it is found that the joints fabricated with magnetic arc oscillation having the superior tensile properties compared to pulsed current welding. The formation of fine grains and higher hardness in fusion zone are the main reasons for the superior tensile properties of these joints

Influence of arc oscillation frequency on tensile properties and microstructural characteristics of magnetic arc oscillation welded AZ31B magnesium alloy joints

Abstract This investigation aims at assessing the impact of magnetic oscillation frequency on tensile properties and the microstructural pattern of gas tungsten arc welded with AZ31B Magnesium alloy joints. Arc oscillation frequencies ranging from 1 Hz to 3 Hz are used to form various levels of five joints. Unlike the other types joints, the joints having the base of arc oscillation frequency of 2 Hz produced greater tensile properties and it happened because of the presence of finer grains and evenly distributed precipitates in the weld region of the joints.

Microstructural refinement of 6061 and 5052 aluminium alloys by arc oscillation

ABSTRACTThe mechanism of the microstructure refinement of metals and alloys (5052 and 6061) by arc oscillating was studied and discussed via the grain size of regular welds and those welded at different oscillation frequencies. In 5052 alloy, fine columnar crystals appeared near the ‘internal fusion line’ during the oscillating arc welding and the grains have been significantly refined by oscillating arc with low and high frequency. However, the grain refinement of 6061 Al alloy was limited during arc oscillating welding due to the different crystal growth pattern at the fusion line and material properties. It is not caused by changing of the grain refinement mechanism but by the difference in the material properties.