Weld microstructure refinement in a 1441 grade aluminium-lithium alloy
01 Aug 1997-Journal of Materials Science (Kluwer Academic Publishers-Plenum Publishers)-Vol. 32, Iss: 15, pp 4117-4126
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.
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TL;DR: In this article, the effect of welding processes such as GTAW, GMAW, and FSW on mechanical properties of AA6061 aluminium alloy was investigated, and it was found that FSW joints of AA 6061 aluminum alloy showed superior mechanical properties compared with GTAW and GMAw joints, and this was mainly due to the formation of very fine, equiaxed microstructure in the weld zone.
Abstract: The present investigation is aimed at to study the effect of welding processes such as GTAW, GMAW and FSW on mechanical properties of AA6061 aluminium alloy. The preferred welding processes of these alloys are frequently gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) due to their comparatively easier applicability and better economy. In this alloy, the weld fusion zones typically exhibit coarse columnar grains because of the prevailing thermal conditions during weld metal solidification. This often causes inferior weld mechanical properties and poor resistance to hot cracking. Friction stir welding (FSW) is a solid phase welding technique developed primarily for welding metals and alloys that heretofore had been difficult to weld using more traditional fusion techniques. Rolled plates of 6 mm thickness have been used as the base material for preparing single pass butt welded joints. The filler metal used for joining the plates is AA4043 (Al-5Si (wt%)) grade aluminium alloy. In the present work, tensile properties, micro hardness, microstructure and fracture surface morphology of the GMAW, GTAW and FSW joints have been evaluated, and the results are compared. From this investigation, it is found that FSW joints of AA6061 aluminium alloy showed superior mechanical properties compared with GTAW and GMAW joints, and this is mainly due to the formation of very fine, equiaxed microstructure in the weld zone.
271 citations
TL;DR: In this paper, an attempt was made to control the formation of Laves phase in alloy 718 gas tungsten arc welds using pulsed current, and the results show that the use of current pulsing refines the fusion zone microstructure, reduces the amount of laves phase and exerts a favourable influence on its morphology and improves the response of the fusion zones to post-weld heat treatment and weld tensile properties.
Abstract: The presence of Nb rich Laves phase in Inconel 718 weld fusion zones is known to be detrimental to weld mechanical properties. In the present study, an attempt was made to control the formation of Laves phase in alloy 718 gas tungsten arc welds using pulsed current. Welds were produced in 2 mm thick sheets of the alloy with constant current and pulsed current and were subjected to post-weld solution treatment at 980°C followed by aging. Detailed microstructural studies and tensile tests at 650°C were conducted. The results show that the use of current pulsing (i) refines the fusion zone microstructure, (ii) reduces the amount of Laves phase and exerts a favourable influence on its morphology and (iii) improves the response of the fusion zone to post-weld heat treatment and weld tensile properties.
168 citations
TL;DR: In this article, the influence of pulsed current TIG welding parameters on tensile properties of AA 6061 aluminium alloy weldments was investigated. And the results showed that pulsed currents can improve the mechanical properties of the welds compared to those of continuous current welds.
165 citations
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
01 Apr 1999-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, gas tungsten-arc welds were produced in two α-β titanium alloys under a variety of conditions including direct current (d.c.) pulsing and alternating current (a.c.).
Abstract: Pulsing of the welding current is one approach for refining the fusion zone grain structure in α – β titanium alloy welds. This paper reports work in which gas tungsten-arc welds were produced in two α – β titanium alloys under a variety of conditions including direct current (d.c.) pulsing and alternating current (a.c.) pulsing. The results show that, while d.c. pulsing did also refine the weld metal β grain structure, the effect of a.c. pulsing was much greater. Current pulsing enhances fluid flow, reduces temperature gradients and causes a continual change in the weld pool size and shape. These effects, which are believed to be responsible for refining the solidification structure, are much stronger in a.c. pulsing than in d.c. pulsing. The observed grain refinement was shown to result in an appreciable increase in fusion zone tensile ductility. Post-weld heat treatment improved ductility both in pulsed and unpulsed welds, but pulsed welds showed greater tensile elongation even in the heat treated condition.
134 citations
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123 citations
01 Sep 1981-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
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
TL;DR: In this paper, the grain structures in two dimensional GTA welds of a number of commercial aluminum alloys have been studied in order to clarify the mechanisms of grain refinement in welds.
Abstract: The grain structures in two dimensional GTA welds of a number of commercial aluminum alloys have been studied in order to clarify the mechanisms of grain refinement in welds. At low welding speeds and heat inputs the structures were either axial (continuous grains along the weld centerline) or stray (intermittent new grains). At higher speeds and heat inputs the structures were generally either columnar to the weld centerline, or contained some equiaxed grains at the center. Regression analyses indicated that both stray grains and equiaxed grains were favored by increased titanium content. In several alloys, titanium-rich compounds, and in one alloy, zirconium-rich compounds were found at the centers of dendrites. It is concluded that both stray and equiaxed grains originate by heterogeneous nucleation, with possible secondary effects due to constitutional undercooling.
61 citations
TL;DR: In this article, columnar grains can be very effective in reducing solidification cracking, provided that they are oriented favorably, and the effect of the arc oscillation pattern, amplitude, and frequency on the formation of alternating columnar grasps and the reduction of solidification cracks in GTA welds of 2014 aluminum alloy was examined and explained.
Abstract: A new mechanism for reducing weld solidification cracking was proposed, based on the concept of the crack path and resistance to crack propagation, and its effectiveness was verified in magnetically oscillated GTA welds of a rather crack susceptible material 2014 aluminum alloy. This mechanism,i.e., alternating grain orientation, was most pronounced in welds made with transverse arc oscillation of low frequency and high amplitude, and solidification cracking was dramatically reduced in these welds. The effect of the arc oscillation pattern, amplitude, and frequency on the formation of alternating columnar grains and the reduction of solidification cracking in GTA welds of 2014 aluminum alloy was examined and explained. The present study demonstrated for the first time that columnar grains can, in fact, be very effective in reducing solidification cracking, provided that they are oriented favorably.
59 citations
Abstract: Lithium-containing aluminium alloys have reduced density and increased elastic modulus compared with conventional aluminium alloys. Many such alloys are currently under development for aircraft applications, which usually involve mechanical fastening. Consequently, the weldability of lithium-containing aluminium alloys is currently receiving relatively little attention. The weldability of lithium-containing aluminium alloys is reviewed. The vast majority of the welding studies performed have been on the Soviet Al-5 wt% Mg-2 wt% Li alloy, 01420. Alloy 01420 and other lithium-containing aluminium alloys are indeed fusion weldable, and weldments having high joint efficiencies have been made.
46 citations