Stan David

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Metals and Ceramics DivisionOak Ridge National Laboratory

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Prediction is very difficult especially

if it is about the future.

Niels Bohr

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Friction Stir Welding ofFriction Stir Welding of

Advanced Materials:Advanced Materials:ChallengesChallenges

D0000710

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

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Significant advances have been made in thelast two decades related to welding processes

y Enhanced application of laser for manufacturing

y Friction Stir Welding

y Hybrid Welding

y Keyhole Plasma Welding

y Magnetic Pulse Weldingy Ultrasonic Welding

y Transient Liquid Phase Joining

y 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 theinvention of electric arc

y Future developments in

welding processes are

expected through

fundamental understandingof physical processes.

FrictionStir

S.A. David and T. DebRoy, Science, v257 pp497-502, 1992

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Friction stir welding process

y 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 heatingthat 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 arapidly evolving technology

y 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.y Challenges:

Understanding the fundamentals of the process

Application to high temperature materials, tool material and design,

complex geometries and dissimilar materials.

y 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/Pmachine is an enabler for concerted R&D

y MTSIntelligent Stir Machine

y Special tool holder with internal cooling from MegaStir for FSW of high-melting

materials and tool alloy development

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FSW R&D at ORNL

y

Tool Materials Developmenty Process development

Welding of Al, Mg, composite, and high-melting materials

Friction stir processing

Friction stir spot welding

y Modeling Residual stress

Materials flow

Microstructure

Weld performance

y Microstructure characterization

y Collaborations

External Partnership (TWI, MegaStir, BYU, Ford, GM, CSIRO)

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Recent tool material development at ORNLshows tremendous potential

ORNL W-based alloy ORNL Ir-based alloy Tool pin holder

y Need more characterization of tool behavior

y Optimization of composition and processing

y Development of other potential alloys

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Steels and Ti alloys have been friction stir weldedsuccessfully using ORNL tool materials

Ti-6-4, t=

SS304, t=

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Ferrite content: 1.57%

Base Metal

Ferrite

Stir Zone

Ferrite content: 3.37%

Sigma phase

Ferrite

Extensive thermomechanical processing caninfluence the phase stability of microstructuresof FSW

y Some evidence of the transformation of ferrite to sigma phase in the stir zone

was found

y Why?

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Friction stir welding is ideally suited for weldingAl 2124- SiC composite

y Laser welding destroys the

microstructure.y In contrast, the base metal

microstructure is retained in the

weld zone after friction stir welding.

FSW

Laser

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Friction stir welding for piping systems is beingdeveloped

y

ORNL is working with industry to applythe friction stir welding process to steel

piping systems

y The first prototype FSW system for piping

system built by MegaStir

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Friction Stir Spot Welding (FSSW) can be amore efficient alternate process to electricresistance spot welding

y FSSW has generated tremendous interests in the automotive industry

Direct replacement of resistance spot welding of Al

y Significant energy and cost savings

Potential for advanced high-strength steels and other high-temperature alloys

y Opportunities in other industries

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Mazda RX-8 Rear Door (Aluminum Panel) is Madeby 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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water

air

Robot Cables

Welding

Gun

Robot

Controller

Welding

cable

Weldingtrans.

Electrode

dresser

junctio

n box

Welding

controller

Welding

Powersupply

Eliminated water, air, and welding powersupplies

Changing from RSW to friction stir spot weldingsystem has significant advantages

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Friction Stir Processing:FSP can modify surface microstructure and improve

properties

yA356 & A319 castings are casting

alloys used in automotive engine,

driveline, and steering components

y Low ductility due to coarse eutectic

microstructures, shrinkage porosity

y Ford interest is for improving

reliability, resistance to failure

Ductility, yield strength, porosity

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FSP produced very uniform distributions of fineparticles in stir zones

y Stir zone microstructure y Boundary between stir zone (left),and base metal (right)

Shrinkage porosity was closed in stir zone

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Condition 0.2% YS, MPa UTS Uniform strain, %

Base avg. 146 161 0.53

FSP avg. 164 296 8.03

Typical tensile test results for A319

3

1

1

tress

a

train

Room temper ture tests at 0.001 s-1

A319 castiAs-cast base metalFriction processed

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FSP increased the fatigue life of A356

y Preliminary results from Ford Scientific Research Laboratory

y Material is being prepared for more extensive testing

Condition Applied strain

Stress

amplitude, ksi

@ life

Neuber stress

range, ksi @

life

Life, # of

reversals

As-cast 0.002 15.5 39.0 7,700

FSP 0.002 19.4 43.9 93,848

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FSW has great potential for repair welding ofirradiated materials

y Gas tungsten arc weld repair of irradiated material can introduce more

problems Helium bubble induced HAZ cracking

Asano et al. J. Nucl. Mat. 264 (1999)1-9 SS304L

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FSW: max He bubble = 69 nmGTAW: max He bubble = 254 nm

Modeling effort at ORNL has shown that FSWdrastically reduces the helium bubble growth,and could be developed as a viable repairtechnology for aging irradiated nuclearcomponents

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Friction Stir Welding Modeling from Process toPerformance

Integrated thermal-mechanical-

metallurgical computational

simulations provide insights to

the performance of welded

structures

Material flow was simulated with

Arbitrary Lagrangian-Eulerian (ALE) finiteelement formulation, which allows for

prediction of weld defect formation under

certain welding conditions.Velocity fieldaround tool pin

Trace Marker

Predicted void location

Void in actual weld

Hardness

Temperature

Residual Stress

Failure line in HAZ

55

Failure Prediction

Under Loading

WeldCenterline

5555

Actual weld

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Simulation captures the weakest link in analuminum friction stir weld

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Neutron scattering facility at ORNL has been usedto investigate residual stress distribution in FSW

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Summary

y ORNL is actively conducting both fundamental and applied R&D in friction

stir welding and processing

y ORNL has some unique facility and capabilities for FSW R&D

Tool material development

Process development

Process modeling

Advanced microstructure investigations

y ORNL is working closely with our partners to advance the FSW/P technology

Academia

Industries International collaborations (TWIand CSIRO)

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Before I came here I was confused

about this subject. Having listened toyour lecture I am still confused, but on

a higher level.

Enrico Fermi

Stan David

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