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Effects of activating flux on titanium alloy welds
2002 (engelsk)Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
Abstract [en]

This year final project was carried out at the Singapore Institute of Manufacturing Technology and presents a comparative study of Tungsten Inert Gas (TIG) and Active-flux TIG (A-TIG) welding of titanium alloys. A series of welding tests were performed in bead-on plate mode for the commonly used Ti-6Al-4V alloy with various welding currents. The work provides useful data for A-TIG welding of titanium alloys and potential industrial applications. The TIG welds without active flux were found to have straight and smooth surfaces, but were also wider and shallower than the corresponding A-TIG welds. To evaluate changes in weld bead profile, the weld penetration, reinforcement and weld width were measured. A-TIG welding generally produced a higher depth to width ratio and around 20% deeper weld penetration than TIG welding. Analysis by X-ray Diffraction (XRD) and Energy Dispersive X-Ray Spectroscopy (SEM/EDX) showed that the active flux consisted mainly of magnesium fluoride (MgF2) and that no detectable amount of flux was absorbed in the welds. Optical microscope studies indicated that there were no major microstructural differences between TIG and A-TIG welds. All grains grew epitaxially from the beta grains into the liquid weld metal. The microstructure consisted of a fine Widmanstätten structure and retained beta or a fine Widmanstätten structure and retained beta and ’ martensite. The lowest welding current produced welds that contained more martensite due to the higher cooling rate and therefore showed a higher hardness than those produced with higher welding current. Short-term corrosion tests were performed to determine the effect of A-TIG welding on the corrosion resistance of the welds. In all cases, the base material had the greatest resistance to corrosion. In the case of NaCl, the base material and welds had approximately the same corrosion rate. However, in H2SO4, the welds corroded more quickly which is thought to be due to the phase changes and grain growth after welding. Although the sulfuric acid was more aggressive for the welds, all welds were still passive.

sted, utgiver, år, opplag, sider
2002.
Emneord [en]
Technology, Welding, titanium, active-flux, Ti-6Al-4V, TIG, A-TIG, GTAW, A-GTAW, corrosion, penetration, reinforcement, microstructure
Emneord [sv]
Teknik
Identifikatorer
URN: urn:nbn:se:ltu:diva-56331ISRN: LTU-EX--02/303--SELokal ID: d1cf2a47-d987-4bb9-8967-920199319c7dOAI: oai:DiVA.org:ltu-56331DiVA, id: diva2:1029718
Fag / kurs
Student thesis, at least 30 credits
Utdanningsprogram
Mechanical Engineering, master's level
Examiner
Merknad
Validerat; 20101217 (root)Tilgjengelig fra: 2016-10-04 Laget: 2016-10-04bibliografisk kontrollert

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Totalt: 283 treff
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