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Journal ArticleDOI

Use of magnetic arc oscillation for grain refinement of gas tungsten arc welds in α–β titanium alloys

01 Jun 1999-Science and Technology of Welding and Joining (Taylor & Francis)-Vol. 4, Iss: 3, pp 151-160
TL;DR: In this article, gas tungsten arc welding was carried out, during which transverse oscillations of the arc were induced through the use of an alternating external magnetic field, and considerable refinement of the fusion zone grain structure was achieved.
Abstract: In an effort to refine the weld metal grain structure in α–β titanium alloys, gas tungsten arc welding was carried out, during which transverse oscillations of the arc were induced through the use of an alternating external magnetic field. At optimum values of oscillation amplitude and frequency in both the alloys investigated, considerable refinement of the fusion zone grain structure was achieved. This could be attributed to factors that include enhanced fluid flow, reduced temperature gradients, and a continually changing weld pool size and shape owing to the action of the imposed magnetic field. The reduction in the prior β grain size was shown to result in a notable increase in fusion zone tensile ductility. Post-weld annealing increased ductility in all cases, but the magnetically treated material continued to show a higher elongation than that of the untreated material even after post-weld heat treatment.
Citations
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Journal ArticleDOI
TL;DR: In this article, the role of the laser parameters such as pulse energy and duration and peak power have been investigated to join 3-mm thick Ti6Al4V using the Lumonics JK760TR Nd:YAG pulsed laser.

329 citations

Journal ArticleDOI
TL;DR: In this article, the effects of pulsed gas tungsten arc welding parameters on the morphology of additive layer manufactured Ti6Al4V has been investigated and it was found that the wire feed rate has a considerable effect on the prior beta grain refinement at a given heat input.
Abstract: The effects of pulsed gas tungsten arc welding parameters on the morphology of additive layer manufactured Ti6Al4V has been investigated in this study. The peak/base current ratio and pulse frequency are found to have no significant effect on the refinement of prior beta grain size. However, it is found that the wire feed rate has a considerable effect on the prior beta grain refinement at a given heat input. This is due to the extra wire input being able to supply many heterogeneous nucleation sites and also results in a negative temperature gradient in the front of the liquidus which blocks the columnar growth and changes the columnar growth to equiaixal growth.

197 citations


Cites background or result from "Use of magnetic arc oscillation for..."

  • ...Sundaresan [3] [4] and Balasubramanian [5] [6] reported that the prior beta grain size of pulsed gas tungsten arc welds in thin Ti6Al4V plate was considerably reduced and equiaxial grains were obtained in fusion zone....

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  • ...5 macrostructure of beta grain size hasn’t been obviously changed as previously reported by the authors [3-6], as indicated in Fig....

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Journal ArticleDOI
TL;DR: In this paper, the improvement of mechanical properties of AA 5456 aluminum alloy welds through pulsed tungsten inert gas (TIG) welding process was investigated and regression models were developed to check the adequacy of the developed models.

138 citations

Dissertation
09 May 2012
TL;DR: In this paper, the influence of the processing conditions on microstructure and texture evolution and their resulting effect on the mechanical properties during additive manufacturing with a Ti6Al4V alloy, using three different techniques, namely, Selective laser melting (SLM), Electron beam selective melting (EBSM), and Wire arc additive manufacturing (WAAM) process.
Abstract: Additive Manufacturing (AM) is an innovative manufacturing process which offers near-net shape fabrication of complex components, directly from CAD models, without dies or substantial machining, resulting in a reduction in lead-time, waste, and cost. For example, the buy-to-fly ratio for a titanium component machined from forged billet is typically 10-20:1 compared to 5-7:1 when manufactured by AM. However, the production rates for most AM processes are relatively slow and AM is consequently largely of interest to the aerospace, automotive and biomedical industries. In addition, the solidification conditions in AM with the Ti alloy commonly lead to undesirable coarse columnar primary ? grain structures in components. The present research is focused on developing a fundamental understanding of the influence of the processing conditions on microstructure and texture evolution and their resulting effect on the mechanical properties during additive manufacturing with a Ti6Al4V alloy, using three different techniques, namely; 1) Selective laser melting (SLM) process, 2) Electron beam selective melting (EBSM) process and, 3) Wire arc additive manufacturing (WAAM) process. The most important finding in this work was that all the AM processes produced columnar ?-grain structures which grow by epitaxial re-growth up through each melted layer. By thermal modelling using TS4D (Thermal Simulation in 4 Dimensions), it has been shown that the melt pool size increased and the cooling rate decreased from SLM to EBSM and to the WAAM process. The prior ? grain size also increased with melt pool size from a finer size in the SLM to a moderate size in EBSM and to huge grains in WAAM that can be seen by eye. However, despite the large difference in power density between the processes, they all had similar G/R (thermal gradient/growth rate) ratios, which were predicted to lie in the columnar growth region in the solidification diagram. The EBSM process showed a pronounced local heterogeneity in the microstructure in local transition areas, when there was a change in geometry; for e.g. change in wall thickness, thin to thick capping section, cross-over?s, V-transitions, etc. By reconstruction of the high temperature ? microstructure, it has been shown that all the AM platforms showed primary columnar ? grains with a ? || Nz fibre texture with decreased texture strength from the WAAM to the EBSM and SLM processes. Due to a lack of variant selection, the room temperature ?-phase showed a weaker transformation ?-texture compared to the primary ?-texture with decreased texture strength in line with the reduction in ?-texture strength.The large ? grains observed in the WAAM process were not significantly affected by changes in the GTAW (Gas Tungsten Arc Welding) process parameters, such as travel speed, peak to base current ratio, pulse frequency, etc. However, an increased wire feed rate significantly improved the grain size. Another important finding from this work was that by combining deformation and AM the grain size was reduced to a greater extent than could be achieved by varying the arc or, heat source parameters. It has been shown that the large columnar ?-grain structure usually seen in the WAAM process, with a size of 20 mm in length and 2 mm in width, was refined down to ~ 150 �m by the application of a modest deformation, between each layer deposited. The EBSM process showed consistent average static tensile properties in all build directions and met the minimum specification required by ISO 5832-3 (for the wrought and annealed Ti6Al4V). The WAAM samples produced using more effective shielding and the standard pulsed GTAW system also showed average static properties that met the minimum specification required by AMS 4985C for investment casting and hipped Ti6Al4V alloy. Overall, the fatigue life of the samples that were produced by AM was very good and showed a better fatigue performance than the MMPDS design data for castings. However, there was a large scatter in the fatigue life due to the effect of pores.

129 citations


Cites methods from "Use of magnetic arc oscillation for..."

  • ...This behaviour has been reported in welding a Ti6Al4V alloy with a pulsed GTAW, but with different process parameters [160, 164, 165]....

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Journal ArticleDOI
TL;DR: In this article, the process characteristics of active flux tungsten inert gas welding and keyhole mode GTAW, two recent developments to GTAW are considered, as is keyholemode plasma arc welding, which is capable of greater penetration and faster processing speeds than conventional GTAW.
Abstract: Titanium alloys used in aerospace structures require joints of high integrity to meet the design requirements. Gas tungsten arc welding (GTAW), laser beam welding (LBW) and electron beam welding (EBW) are all processes capable of creating fusion welded joints. Gas tungsten arc welding offers the potential to achieve welds of equal quality to EBW or LBW at much lower capital costs; however, the application of GTAW involves gaining an understanding of the complex process characteristics. This paper reviews the process characteristics for GTAW titanium alloys and compares these characteristics with EBW and LBW titanium alloys. The characteristics of active flux tungsten inert gas welding and keyhole mode GTAW, two recent developments to GTAW, are considered, as is keyhole mode plasma arc welding. These variants are capable of greater penetration and, in some cases, faster processing speeds than conventional GTAW. Finally, the current knowledge of weld microstructural development in cast and wrought α...

93 citations

References
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Journal ArticleDOI
TL;DR: In this article, a computer simulation of weld pool fluid flow and its effect on weld penetration was carried out, with three driving forces for fluid flow being considered: the buoyancy force, the electromagnetic force, and the surface tension gradient at the weld pool surface.
Abstract: Weld pool fluid flow can affect the penetration of the resultant weld significantly. In this work, the computer simulation of weld pool fluid flow and its effect on weld penetration was carried out. Steady-state, 2-dimensional heat and fluid flow in stationary arc welds were computed, with three driving forces for fluid flow being considered: the buoyancy force, the electromagnetic force, and the surface tension gradient at the weld pool surface. The computer model developed agreed well with available analytical solutions and was consistent with weld convection phenomena experimentally observed by previous investigators and the authors. The relative importance of the influence of the three driving forces on fluid flow and weld penetration was evaluated, and the role of surface active agents was discussed. The effects of the thermal expansion coefficient of the liquid metal, the current density distribution in the workpiece, and the surface tension temperature coefficient of the liquid metal on weld pool fluid flow were demonstrated. Meanwhile, a new approach to free boundary problems involving simultaneous heat and fluid flow was developed, and the effort of computation was reduced significantly.

233 citations

Journal ArticleDOI
TL;DR: In this paper, a wide range of fundamental knowledge of solidification processes is applied to the study of fusion-weld solidification, including inoculants, stimulated surface nucleation, dynamic grain refinement, and arc modulation.
Abstract: To an increasing extent the wide range of fundamental knowledge of solidification processes is being applied to the study of fusion-weld solidification. Initially this fundamental knowledge is surveyed concisely and those areas of particular importance to weld-pool solidification are indentified. This is followed by an examination of phenomenological studies of the solidification behaviour of fusion welds in which particular attention is given to factors influencing the development of the fusion-zone structure. Then, the ways in which the metallurgical structure of the fusion zone influences the mechanical properties of the weldment are reviewed. Attention is then given to methods of controlling the fusion-zone structure by using inoculants, stimulated surface nucleation, dynamic grain refinement, and arc modulation. The gains and advantages which accrue from the way in which structure control affects properties are then considered. The review concludes with a discussion of likely future developme...

119 citations

Journal ArticleDOI
TL;DR: The mechanisms of grain refinement have been examined for magnetically stirred gas tungsten arc (GTA) welds completely penetrating thin sheets of several aluminum alloys in this article.
Abstract: The mechanisms of grain refinement have been examined for magnetically stirred gas tungsten arc (GTA) welds completely penetrating thin sheets of several aluminum alloys. Grain refinement in unstirred welds may be brought about by adding sufficient titanium to produce heterogeneous nucleation by Ti-rich particles. In some alloys magnetic stirring is shown to extend the range of welding conditions which produce a partially equiaxed structure, and to widen the equiaxed fraction of partially equiaxed welds. This is attributed to magnetic stirring lowering the temperature gradient, allowing nucleation and growth of Al-rich grains further ahead of the columnar interface growing in from the fusion boundaries. In alloys with low Ti levels, magnetic stirring may cause refinement by sweeping grains from the partially molten zone ahead of the advancing solidification interface. This mechanism requires that the partially molten zone be sufficiently wide, and that the grain size in this zone remain small.

106 citations

Journal ArticleDOI
TL;DR: In this paper, the weld beads obtained under (i) continuous current (CC), (ii) pulsed current (PC), and (iii) arc oscillation (AO) conditions for their macro- and microstructural details were compared.
Abstract: Clad 2 mm thick sheets of Russian 1441 grade Al-Li alloys were welded using a gas tungsten arc welding process (GTAW). Comparisons were made between the weld beads obtained under (i) continuous current (CC), (ii) pulsed current (PC), and (iii) arc oscillation (AO) conditions for their macro- and microstructural details. In the case of CC GTAW, sound welds could be produced only under a narrow range of welding parameters. Centre line cracks, which occurred in CC GTAW welds under certain conditions, were halted by switching to PC or AO conditions while the welding was in progress. Microstructural refinement was significant in the case of PC and AO GTA welding.

105 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of arc oscillation on grain structure and solidification cracking in GTA welds of 5052 aluminum alloy was investigated using a four-pole magnetic arc oscillator and a modified fishbone crack test.
Abstract: The effect of arc oscillation on grain structure and solidification cracking in GTA welds of 5052 aluminum alloy was investigated using a four-pole magnetic arc oscillator and a modified fish-bone crack test. Two different mechanisms of crack reduction were identified: one in the low frequency range of arc oscillation and the other in the high frequency range. The former was the alteration of the orientation of columnar grains, while the latter was grain refining. Neither mechanism was operative in the intermediate frequency range and solidification cracking was severe, especially when the amplitude of arc oscillation was small. Alteration of grain orientation was obtained in welds made with transverse and circular arc oscillations, but not longitudinal arc oscillation. Grain refining, on the other hand, was achieved in welds made with all three types of arc oscillation patterns. The differences between the response of alloy 5052 to arc oscillation and that of alloy 2014 observed previously were discussed.

84 citations