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Study of Embrittled Friction-Stir-Welds

[+] Author Affiliations
Muhammad A. Wahab, David Taylor

Louisiana State University, Baton Rouge, LA

Efstathios Meletis

University of Texas at Arlington, Arlington, TX

Paper No. IMECE2009-13086, pp. 161-167; 7 pages
doi:10.1115/IMECE2009-13086
From:
  • ASME 2009 International Mechanical Engineering Congress and Exposition
  • Volume 14: Processing and Engineering Applications of Novel Materials
  • Lake Buena Vista, Florida, USA, November 13–19, 2009
  • Conference Sponsors: ASME
  • ISBN: 978-0-7918-4387-1 | eISBN: 978-0-7918-3863-1
  • Copyright © 2009 by ASME

abstract

A reduction in mechanical properties has been observed in Friction-Stir-Welded (FSW) Aluminum panels. This reduction in strength has generally been attributed to Residual Oxide Defect (ROD). From NASA experience it was also found that certain processing parameters would yield these reduced mechanical properties. The strength of FSW Aluminum panels generally decreases with increasing tool travel rate, decreasing rotation speed, and offset of the weld seam to the retreating side of the FSW tool. The microstructure of welds exhibiting these strength reduction as well as welds that behaved as expected were examined to determine microstructural effects of processing parameters. Therefore the evolutions of microstructural properties are immensely important to understand and evaluate to avoid any catastrophic failures due to the defects arising from welding operations. Scanning Electron Microscopy shows that these weld conditions are accompanied by large precipitates along the grain boundary for both AA-2219 and AA-2195 FSW welded samples. Transmission Electron Microscopy (TEM) also shows the precipitates to be “theta particles (Al2 Cu)” and intermetallics in the AA-2219; and T1 (Al2 CuLi), and TB particles in the AA-2195. The large size and heavy distributions of these precipitates, especially on the advancing side of the weld seam may influence these properties. It is determined that the existence of ROD in the samples must be analyzed systematically and carefully through the evolutions of microstructures, if catastrophic failures are to be avoided during service conditions. A more complete understanding of this phenomenon is necessary to ensure consistent and predictable weld properties thereby reducing or eliminating the risk of unforeseen failures.

Copyright © 2009 by ASME

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