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Applications: Titanium Friction Stir Weld

 
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Principle
   - make cut
   - measure surface
   - calculate stress
Validations
Applications
   - bent beam
   - weld plate
   - quenched steel
   - impacted plate
   - alum. forging
   - friction stir weld
>    - Ti FSW
   - Railroad rails
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Residual Stress
Conferences
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M.B. Prime, T.J. Lienert, W.L. Stellwag, R.S. Casey, “Residual Stress Measurement in Friction Stir Welded Ti-6Al-4V,” Fabtech International and AWS Welding Show 2005, November 13–16, 2005, Chicago, Illinois. (LA-UR-05-8693)

Results:

Residual longitudinal stresses

  • Looks more like fusion welding stresses than the two peak distribution typical of FSW of aluminum alloys
  • The stir zone or nugget exhibited residual tensile stress. A single peak of tensile stresses > 400 MPa was observed slightly below the surface corresponding to the shoulder of the tool.
  • The stresses were asymmetric with higher stresses on the advancing side of the weld.

Friction Stir Welding:

  • 0.285” thick Ti-6Al-4V plate - mill annealed
  • FSW at 3.75 ipm and 275 RPM using inert gas box with sliding top.
  • CP Tungsten tool with 0.75” diameter shoulder & 0.31” diameter pin (no threads). Cooled tool holder.
FSW of Ti

 

Macro metallography :

  • Weld region displayed three microstructurally distinct zones
    • Stir zone or nugget.
    • HAZ (Heat-Affected Zone) or TMAZ (Thermo-Mechanically Affected Zone)
    • Base metal
  • Some Tungsten from tool observed
Macro regions

Microstructure:

Base metal microstructure

  • Base metal
  • Fine equiaxed grains of α
    phase
  • with small amounts of intergranular β phase

Stir/HAZ Boundary

  • Stir zone/HAZ boundary

Stir zone microstructure

  • Stir zone:
  • GB α phase
  • with fine
    acicular α in prior β grains

 

Microhardness :

  • 1 kg load & 15 seconds dwell
  • Higher hardness in stir zone
Hv Microhardness map

 

Contour Experiment:

  • Part was clamped in special fixture to minimize movement during cutting (see on picture on cutting page)
  • Cut in wire EDM machine using 50 µm (0.002") diameter tungsten wire.
  • Surface contour measured using laser scanner
  • Peak-to-valley about 190 µm not including noise in data:
Measured surface contour

Calculate Stress using FEM

  • Make 3-D model of plate after cut
  • Start with flat surface
  • Using displacement boundary conditions, force cut surface to opposite of measured contour
  • Extract stresses normal to surface.
Deformed 3D FE model

 

 

 

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Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA
contact: Mike Prime at prime@lanl.gov | Copyright & Disclaimer
U.S. patent 6,470,756 | Last Modified: November 23, 2009

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