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Prediction is very difficult especially if it
is about the future. Niels Bohr
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Friction Stir Welding of Advanced Materials
Challenges
S. A David and Zhili Feng Materials Joining
Group Metals and Ceramics Division Oak Ridge,
TN 9th Materials Day in Graz In Honor of
Professor H. Cerjak November 19, 2004 Graz,
Austria
D0000710
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Significant advances have been made in the last
two decades related to welding processes

• Enhanced application of laser for manufacturing
• Friction Stir Welding
• Hybrid Welding
• Keyhole Plasma Welding
• Magnetic Pulse Welding
• Ultrasonic Welding
• Transient Liquid Phase Joining
• Future Directions
• Processes such as FSW, Hybrid and others will be
  used extensively in energy, transportation and
  ship building etc..
• Application of nanoscience and technology for
  materials joining.

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Growth of welding processes after the invention
of electric arc
Friction Stir

• Future developments in welding processes are
  expected through fundamental understanding of
  physical processes.

S.A. David and T. DebRoy, Science, v257
pp497-502, 1992
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Friction stir welding process

• Friction Stir Welding (FSW) is a new, novel
  solid-state joining process. A specially
  designed tool rotates and traverses along the
  joint line, creating frictional heating that
  softens a column of material underneath the tool.
  The softened material flows around the tool
  through extensive plastic deformation and is
  consolidated behind the tool to form a
  solid-state continuous joint.

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Friction stir welding and processing is a rapidly
evolving technology

• Invented by TWI in early 1990s
• A huge success for joining Al alloys and other
  low-melting temperature materials that are
  difficult to fusion-weld
• Solid state joining process, no filler metal,
  joint strengths are better, low distortion and
  residual stresses.
• Challenges
• Understanding the fundamentals of the process
• Application to high temperature materials, tool
  material and design, complex geometries and
  dissimilar materials.
• New technology frontiers
• High temperature and high-performance materials
  joining
• Friction stir processing
• Friction stir spot welding

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Oak Ridge National Laboratorys FSW/P machine is
an enabler for concerted RD

• MTS Intelligent Stir Machine
• Special tool holder with internal cooling from
  MegaStir for FSW of high-melting materials and
  tool alloy development

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FSW RD at ORNL

• Tool Materials Development
• Process development
• Welding of Al, Mg, composite, and high-melting
  materials
• Friction stir processing
• Friction stir spot welding
• Modeling
• Residual stress
• Materials flow
• Microstructure
• Weld performance
• Microstructure characterization
• Collaborations
• External Partnership (TWI, MegaStir, BYU, Ford,
  GM, CSIRO)

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Recent tool material development at ORNL shows
tremendous potential
ORNL W-based alloy
ORNL Ir-based alloy
Tool pin holder

• Need more characterization of tool behavior
• Optimization of composition and processing
• Development of other potential alloys

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Steels and Ti alloys have been friction stir
welded successfully using ORNL tool materials
Ti-6-4, t¼
SS304, t¼
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Extensive thermomechanical processing can
influence the phase stability of microstructures
of FSW
Ferrite content 1.57

• Some evidence of the transformation of ferrite to
  sigma phase in the stir zone was found
• Why?

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Friction stir welding is ideally suited for
welding Al 2124- SiC composite
FSW
Laser

• Laser welding destroys the microstructure.
• In contrast, the base metal microstructure is
  retained in the weld zone after friction stir
  welding.

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Friction stir welding for piping systems is being
developed

• ORNL is working with industry to apply the
  friction stir welding process to steel piping
  systems
• The first prototype FSW system for piping system
  built by MegaStir

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Integrating FSW with other processes (hybrid) can
improve process efficiency and tool life
4kW CW NdYAG laser with fiber optic delivery

• Integrate laser or high-power infrared heating
  with FSW to improve welding speed and tool life
  in welding of high-temperature materials

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Friction Stir Spot Welding (FSSW) can be a more
efficient alternate process to electric
resistance spot welding

• FSSW has generated tremendous interests in the
  automotive industry
• Direct replacement of resistance spot welding of
  Al
• Significant energy and cost savings
• Potential for advanced high-strength steels and
  other high-temperature alloys
• Opportunities in other industries

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Mazda RX-8 Rear Door (Aluminum Panel) is Made by
FSSW

• Robotic FSSW system replaces resistance spot
  welding system

(Courtesy of Ford)
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Friction stir spot weld of Al 6111
Front side
Back side
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Changing from RSW to friction stir spot welding
system has significant advantages
Welding Power supply
air

• Eliminated water, air, and welding power supplies

water
Robot Controller
Welding controller
Welding trans.
Welding Gun
Welding cable
junction box
Electrode dresser
Robot Cables
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Friction stir spot welding system

• Eliminated water, air, and welding power
  supplies.
• 99 energy saving (vs. RSW, according to Mazda)
• 40 investment reduction (vs. RSW)

(Courtesy of Ford)
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Friction Stir Processing FSP can modify surface
microstructure and improve properties

• A356 A319 castings are casting alloys used in
  automotive engine, driveline, and steering
  components
• Low ductility due to coarse eutectic
  microstructures, shrinkage porosity
• Ford interest is for improving reliability,
  resistance to failure
• Ductility, yield strength, porosity

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FSP produced very uniform distributions of fine
particles in stir zones

• Stir zone microstructure

• Boundary between stir zone (left), and base metal
  (right)

Shrinkage porosity was closed in stir zone
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Typical tensile test results for A319
Condition 0.2 YS, MPa UTS Uniform strain,
Base avg. 146 161 0.53
FSP avg. 164 296 8.03
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FSP increased the fatigue life of A356
Condition Applied strain Stress amplitude, ksi _at_ ½ life Neuber stress range, ksi _at_ ½ life Life, of reversals
As-cast 0.002 15.5 39.0 7,700
FSP 0.002 19.4 43.9 93,848

• Preliminary results from Ford Scientific Research
  Laboratory
• Material is being prepared for more extensive
  testing

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FSW has great potential for repair welding of
irradiated materials
SS304L
Asano et al. J. Nucl. Mat. 264 (1999)1-9

• Gas tungsten arc weld repair of irradiated
  material can introduce more problems Helium
  bubble induced HAZ cracking

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Modeling effort at ORNL has shown that FSW
drastically reduces the helium bubble growth, and
could be developed as a viable repair technology
for aging irradiated nuclear components
FSW max He bubble 69 nm
GTAW max He bubble 254 nm
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Friction Stir Welding Modeling from Process to
Performance

• Material flow was simulated with Arbitrary
  Lagrangian-Eulerian (ALE) finite element
  formulation, which allows for prediction of weld
  defect formation under certain welding conditions.

Hardness

• Integrated thermal-mechanical-metallurgical
  computational simulations provide insights to the
  performance of welded structures

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Simulation captures the weakest link in an
aluminum friction stir weld
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Neutron scattering facility at ORNL has been used
to investigate residual stress distribution in
FSW
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Summary

• ORNL is actively conducting both fundamental and
  applied RD in friction stir welding and
  processing
• ORNL has some unique facility and capabilities
  for FSW RD
• Tool material development
• Process development
• Process modeling
• Advanced microstructure investigations
• ORNL is working closely with our partners to
  advance the FSW/P technology
• Academia
• Industries
• International collaborations (TWI and CSIRO)

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Before I came here I was confused about this
subject. Having listened to your lecture I am
still confused, but on a higher level.
Enrico Fermi