Mechanism and Microstructure of Oxide Fluxes for Gas Tungsten Arc Welding of Magnesium Alloy
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magnesium alloys have the potential to replace steel and aluminum in many structural applications.[3,4] Thus, magnesium alloys have already found considerable applications in aerospace, aircraft, automotive, electronics, and other fields, especially magnesium die castings in the automotive industry.[5] However, the wider application of magnesium alloys needs reliable welding processes. Magnesium alloy components may be joined using mechanical fasteners as well as a variety of welding methods including tungsten-arc inert gas (TIG), metal-arc inert gas, plasma arc, electron, laser, friction,[6] adhesive,[5] explosion, stud, ultrasonic,[7] and spot welding.[8] Improvements in weld penetration have long been sought in gas tungsten arc welding because TIG welding has a good weld appearance and high quantity, but relatively shallow penetration, especially in the single-pass welding process for stainless steel, titanium alloys, and magnesium alloys. There are many methods to improve TIG welding penetration and,
L.M. LIU, Professor, Z.D. ZHANG, Doctor, G. SONG, Doctor, and L. WANG, Professor, are with the State Key Laboratory of Material Surface Modification by Laser, Ion, and Beams, School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024, People’s Republic of China. Contact e-mail: liulm@ dlut.edu.cn Manuscript submitted July 14, 2006. Article published online March 27, 2007. METALLURGICAL AND MATERIALS TRANSACTIONS A
consequently, production. One of the most notable examples is the use of activating flux with the TIG welding process.[9–13] The TIG flux welding based on various oxides, halides, and metal powder compounds is being used more and more in industry. A number of studies regarding flux-assisted gas tungsten arc welding (A-TIG) have been published. In the mid-1960s, research showed weld penetration could be augmented as much as 3 times when the base materials were coated with fluxes.[14,15] Such fluxes remain interesting today because they allow full-penetration welding at greater rates while still employing the inexpensive and clean gas tungsten arc as the heat source. To date, however, fluxes have been developed only for joining titanium alloys[15–18] and steels,[19,20] and their compositions are not published. Several mechanisms for the augmented penetration observed in A-TIG welding have been given.[18–21] The relative importance of each mechanism is a function of the chemical composition of the flux and bade metal, as well as the process parameters. Although not entirely resolved, the mechanism of arc constriction that raises the current density and creates welds with greater depthto-width ratios has often been invoked.[11,22] Because the flux also chemically interacts with the molten material, a surface-energy contribution that originates a Marangoni flow has also been proposed.[23,24] Some research works on the A-TIG welding for magnesium alloy were done by Marya[25,26] and Liuliming.[27–30] In this study, five different kinds of oxide fluxes we
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