Paper Title:
Epitaxial Grain Growth during Surface Modification of Friction Stir Welded Aerospace Alloys by a Pulsed Laser System
  Abstract

The liquid film re-growth behaviour resulting from pulsed laser surface melting (LSM) has been investigated for typical 2xxx, and 7xxx aerospace alloys, both on parent plate and friction stir welded (FSW) joints. In Zr free alloys, as a result of the high growth rate and steep thermal gradient, the melted layer re-grew with a stable front, epitaxially, from the parent subsurface grains. This caused a thin coarse grained solidified layer to form over the parent material, thermomechanically affected zone (TMAZ) and heat affected zone (HAZ), and fine columnar grains to develop over the FSW nugget zone of the same order in width as the nugget grain size. In the case of the Zr containing alloys, a very fine columnar grain structure was found over the entire surface, independent of the subsurface grain structure. This has been shown to occur by growth selection from a band of nanoscale Al grains epitaxially nucleated on Al3Zr dispersoids, at the melt solid interface, that had not fully dissolved in the melt.

  Info
Periodical
Materials Science Forum (Volumes 519-521)
Edited by
W.J. Poole, M.A. Wells and D.J. Lloyd
Pages
1169-1174
DOI
10.4028/www.scientific.net/MSF.519-521.1169
Citation
P. Ryan, P. B. Prangnell, S. W. Williams, "Epitaxial Grain Growth during Surface Modification of Friction Stir Welded Aerospace Alloys by a Pulsed Laser System", Materials Science Forum, Vols. 519-521, pp. 1169-1174, 2006
Online since
July 2006
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