Oak Ridge National Laboratory is conducting research and development on friction stir welding and processing. Some key areas of R&D include tool material development, process development for joining advanced materials, process modeling, and microstructure characterization. Friction stir welding has potential applications in energy, transportation, and shipbuilding industries.

1. “ Prediction is very difficult – especially if it is about the future.” – Niels Bohr

2. Friction Stir Welding of Advanced Materials: Challenges 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

3. 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.

4. Growth of welding processes after the invention of electric arc Future developments in welding processes are expected through fundamental understanding of physical processes. Friction Stir S.A. David and T. DebRoy, Science, v257 pp497-502, 1992

5. 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.

6. 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

7. Oak Ridge National Laboratory’s FSW/P machine is an enabler for concerted R&D MTS Intelligent Stir Machine Special tool holder with internal cooling from MegaStir for FSW of high-melting materials and tool alloy development

8. FSW R&D 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)

9. Recent tool material development at ORNL shows tremendous potential Need more characterization of tool behavior Optimization of composition and processing Development of other potential alloys ORNL W-based alloy ORNL Ir-based alloy Tool pin holder

10. Steels and Ti alloys have been friction stir welded successfully using ORNL tool materials Ti-6-4, t=¼” SS304, t=¼”

11. Extensive thermomechanical processing can influence the phase stability of microstructures of FSW Some evidence of the transformation of ferrite to sigma phase in the stir zone was found Why? Ferrite content: 1.57% Base Metal Ferrite Stir Zone Ferrite content: 3.37% Sigma phase Ferrite

12. Friction stir welding is ideally suited for welding Al 2124- SiC composite Laser welding destroys the microstructure. In contrast, the base metal microstructure is retained in the weld zone after friction stir welding. FSW Laser

13. 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

14. Integrating FSW with other processes (hybrid) can improve process efficiency and tool life Integrate laser or high-power infrared heating with FSW to improve welding speed and tool life in welding of high-temperature materials 4kW CW Nd:YAG laser with fiber optic delivery

15. 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

16. Mazda RX-8 Rear Door (Aluminum Panel) is Made by FSSW Robotic FSSW system replaces resistance spot welding system (Courtesy of Ford)

17. Friction stir spot weld of Al 6111 Front side Back side

18. Changing from RSW to friction stir spot welding system has significant advantages water air Robot Cables Welding Gun Robot Controller Welding cable Welding trans. Electrode dresser junction box Welding controller Welding Power supply Eliminated water, air, and welding power supplies

19. 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) Robot Cables Welding Gun Robot controller

20. 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

21. 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

22. Typical tensile test results for A319 8.03 296 164 FSP avg. 0.53 161 146 Base avg. Uniform strain, % UTS 0.2% YS, MPa Condition

23. FSP increased the fatigue life of A356 Preliminary results from Ford Scientific Research Laboratory Material is being prepared for more extensive testing 93,848 43.9 19.4 0.002 FSP 7,700 39.0 15.5 0.002 As-cast Life, # of reversals Neuber stress range, ksi @ ½ life Stress amplitude, ksi @ ½ life Applied strain Condition

24. FSW has great potential for repair welding of irradiated materials 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

25. 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

26. Friction Stir Welding Modeling – from Process to Performance Integrated thermal-mechanical-metallurgical computational simulations provide insights to the performance of welded structures 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 Velocity field around tool pin Trace Marker Predicted void location Void in actual weld Temperature Residual Stress Failure line in HAZ 55° Failure Prediction Under Loading Weld Centerline 55° Actual weld

27. Simulation captures the weakest link in an aluminum friction stir weld

28. Neutron scattering facility at ORNL has been used to investigate residual stress distribution in FSW

29. Summary ORNL is actively conducting both fundamental and applied R&D in friction stir welding and processing ORNL has some unique facility and capabilities for FSW R&D 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)

30. “ 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