Parameterization of Friction Stir Welding of Al 6061/SiC/17.5p

1. Parameterization of Friction Stir Welding of Al 6061/SiC/17.5p Vanderbilt University Welding Automation Laboratory Tracie Prater Dr. George Cook Dr. Al Strauss Dr. Jim Davidson Mick Howell

2. Metal Matrix Composites (MMCs) • Composite material comprised of two parts: • Continuous metal matrix • Reinforcing particles • Classification scheme • four digit number • type of reinforcement • percentage reinforcement • form of reinforcement: whiskers (w) or particles (p)

3. Industrial applications of Al-MMCs • Tank armors • Structural components of aircraft • Bicycle frames • Engine cylinders

4. Previous work in fusion welding of Al-MMCs • Assessment of problems inherent in welding MMCs using fusion techniques published by Storjohann, et. al. • compares GTA, EB, and LB with FSW welds of Aluminum alloy reinforced with SiC whiskers • presence of deleterious θ phase (Al4C3) detected in all fusion-welded joints • porosities in HAZ • dissolution of SiC whiskers • can mitigate these effects through careful control of heat input Microstructure of LB weld1 1. Storjohann, D., O.M. Barabash, S.S. Babu and S.A. David, et. al. “Fusion and Friction Stir Welding of Aluminum Metal Matrix Composites.” Metallurgical and Materials Transactions: A: Physical Metallurgy and Materials Science 36A (2005): 3237-3247.

5. Why FSW? • improved orientation and shape of reinforcement in finished joint • lower temperature process – absence of melting • repeatability Spatial orientation of SiC whiskers in FSW weld1 SiC reinforcement particles post-weld1 1. Storjohann, D., O.M. Barabash, S.S. Babu and S.A. David, et. al. “Fusion and Friction Stir Welding of Aluminum Metal Matrix Composites.” Metallurgical and Materials Transactions: A: Physical Metallurgy and Materials Science 36A (2005): 3237-3247.

6. Overall trends in FSW of MMCs • severe tool wear • upper limit of joint efficiencies in range of 60 to 70 percent • changes in pre and post weld size and distribution of reinforcement particles • weldability of a particular MMC is inversely proportional to percentage reinforcement • narrow weld envelope 2. Fernandez, G.J. and L.E. Murr.“Characterization of tool wear and weld optimization in the friction-stir welding of cast aluminum 359+20% SiC metal matrix composite.” Materials Characterization 52 (2004): 65-75.

7. Experimental Setup • Milwaukee #2K Universal Milling Machine modified for FSW • 9 in x 3 in x ¼ in wide samples – butt weld configuration • clamping system • tool rigidly mounted using locking set screw • load and torque data recorded by Kistler rotating quartz 4-component dynamometer • travel rate, rotation speed, plunge depth, and tool position controlled through custom-built GUI

8. 20 HP motor V-belt and pulley system Vertical head Kistler dynamometer Locking set screw Backing plate

9. Design developed by The Welding Institute (TWI) Non-cylindrical smooth probe which is nearly triangular in shape Research by TWI indicates TrivexTM has potential to reduce forces Probe measures .25” at widest point and .235” in length; 3 degree taper TrivexTM tool design Side view of tool Top view of probe

10. Trivex results: non-reinforced Aluminum alloy • Data used as baseline for comparison with metal matrix composites • characterization of x, y, and z forces as function of rotation and travel speed • Tensile tests and microscopy used to parameterize Trivex tool on unreinforced Aluminum 6061

16. Tool wear study on reinforced Al alloy • 4 parameter sets chosen to assess influence of travel speed and rotation speed on wear rate • 1000 rpm, 4 ipm • 1000 rpm, 10 ipm • 1350 rpm, 4 ipm • 1350 rpm, 10 ipm • Shadowgraph of each tool taken after every 9 inches of weldment; dimensions also recorded

17. 1350 rpm, 4 ipm 0 in 9 in 18 in 27 in 36 in 1000 rpm, 4 ipm 0 in 9 in 18 in 27 in 36 in

18. 1000 rpm, 10 ipm 0 in 9 in 18 in 27 in 36 in 1350 rpm, 10 ipm 0 in 9 in 36 in

19. Reduction in probe diameter

20. Reduction in probe length

21. Summary of wear results • Threshold beyond which no wear occurs (referred to as the “self optimized shape”)3 • Welds with higher travel speeds result in less wear • Compromise which much be negotiated in joining MMCs: welding speeds must be slow enough to generate sufficient plastic deformation, yet fast enough to mitigate severe tool wear 1350 rpm @ 10 ipm 1000 rpm @ 10 ipm 3. Prado, R.A., L.E. Murr, K.F. Soto and J.C. McClure. “Self-optimization in tool wear for friction-stir welding of Al 6061+20% Al2O3 MMC.” Materials Science and Engineering 349 (2003): 156-165.

22. MMC Weld Matrix using self-optimized tool • .009” plunge depth • 1 degree tilt angle • Rotation speeds: 500, 750, 1000, 1250, 1500 rpm • Travel rate: 3, 5, 7, 9 ipm • Inconsistent load and torque data presumably due to misalignment and/or gapping

23. Results: MMC Weld Matrix using self-optimized probe defect apparatus limit “defect free”

24. Diamond Coating by Chemical Vapor Deposition (CVD) • Objective is to test CVD as a means of creating superabrasive tools for welding of MMCs • Substrate is coated in plasma chamber containing methane and hydrogen gas • Two activation reactions govern coating process • Same process used to grow carbon nanotubes

25. Diamond formation by CVD • Deryagin model of coating process4 • Carbon coalesces on substrate surface – transport rate of C is reduced • Diamond nucleus is formed when layer has grown to critical size • Plasma increases reaction rate 4. Deryagin, B.V. and D.V. Fedosayev. “The Growth of diamond and graphite from the gas phase.” Surface and Coatings Technology 38 (1989): 131-248.

26. Tool design • Choice of material dictated by environment of coating chamber • Size of chamber also necessitated two-part tool design • Molybdenum probe and shoulder manufactured by Midwest Tungsten of Chicago, IL • Press fit into 01 steel cylinder after coating

27. SEM images of coating

28. Previous VUWAL results for smooth probe CVD-Moly tool on Al-MMC

29. Future research • Comparison of tool wear and forces for coated and uncoated Trivex tool in welding of MMCs • Tensile tests of MMC joints • Radiography • Extend research to include other composite materials

30. References 1. Storjohann, D., O.M. Barabash, S.S. Babu and S.A. David, et. al. “Fusion and Friction Stir Welding of Aluminum Metal Matrix Composites.” Metallurgical and Materials Transactions: A: Physical Metallurgy and Materials Science 36A (2005): 3237-3247. 2. Fernandez, G.J. and L.E. Murr. “Characterization of tool wear and weld optimization in the friction-stir welding of cast aluminum 359+20% SiC metal matrix composite.” Materials Characterization 52 (2004): 65-75. 3. Prado, R.A., L.E. Murr, K.F. Soto and J.C. McClure. “Self-optimization in tool wear for friction-stir welding of Al 6061+20% Al2O3 MMC.” Materials Science and Engineering 349 (2003): 156-165. 4. Deryagin, B.V. and D.V. Fedosayev. “The Growth of diamond and graphite from the gas phase.” Surface and Coatings Technology 38 (1989): 131-248.

31. Acknowledgements • UTSI • Vanderbilt University Machine Shop • Vanderbilt University Diamond Fabrication Lab • sp3, Inc. • DWA Composites • Midwest Tungsten • Drs. George Cook, Jim Davidson, Mick Howell, Al Strauss, Tom Lienert, James Whitting