Argon-Hydrogen Shielding Gas Mixtures for Activating Flux-Assisted Gas Tungsten Arc Welding
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GAS tungsten arc welding (GTAW) is applicable for welding on nearly all metals and alloys because it provides the excellent and uniform quality required for industrial applications. The use of GTAW for thick materials has been limited by its small deposition rate and very low efficiency.[1,2] The inability of GTAW to produce welds with a deep penetration limits the thickness of the material that can be welded reliably, with the penetration generally being around 2 mm to 3 mm.[3,4] Materials thicker than 3 mm typically require proper joint preparation and multiple weld passes.[5] In addition, GTAW welds also are affected by cast-to-cast variations in the composition of certain residual elements.[6–8] In practice, variable weld penetration is encountered most often in stainless steel, even though this phenomenon occurs in other materials as well.[9] To overcome the various problems and to increase penetration depth, a modification of the GTAW process both improves the quality and assures a much better economic efficiency. Activating flux GTAW first was proposed by the Paton Electric Welding Institute in the 1960s.[10,11] Activating flux is a mixture of inorganic material suspended in a volatile medium, which then is applied in a thin layer to the surface of the part or joint before it is welded. Immediate savings can result in reduced joint preparation costs, the ability to produce single-pass, full-penetration welding, a high welding speed, consistent quality, and excellent bead appearance.[12–14] Besides, many researchers[15–17] have applied HER-YUEH HUANG, Assistant Professor, is with the Department of Materials Science and Engineering, National Formosa University, Yunlin 632, Taiwan R.O.C. Contact e-mail: huanghy@ nfu.edu.tw Manuscript submitted February 3, 2010. Article published online July 7, 2010 METALLURGICAL AND MATERIALS TRANSACTIONS A
activating flux on laser welding, electron welding, etc. The deep penetration action of activating fluxes also can be obtained in electron and laser beam melt runs, which is welding without the usual arc. The fluxes that have been developed for joining titanium alloys, magnesium alloys, aluminum alloys, steels etc. are almost always fluorides, oxides, or chlorides.[4,6,18–21] Therefore, the chemical composition of a flux and an evaluation of its properties for compatibility are of importance. In GTAW, a shielding gas is employed to protect the weld and the tungsten electrode from degradation or oxidation. Argon is the most commonly used for this process because it has a relatively low spatter and a stable arc.[22] Therefore, the argon-hydrogen shielding gas mixture is used to increase the welding heat and to help control the weld bead profile.[23–25] Adjusting the composition of the shielding gas also influences the distribution of heat to the weld, consequently affecting the weld bead geometry.[26] Adding hydrogen to the argon-based shielding gas influences the heat input of the activating flux GTAW. However, only a few published reports are available on the shielding gas composition
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