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

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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 ? 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.
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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 35920 SiC metal matrix composite.
Materials Characterization 52 (2004) 65-75.
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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
  

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20 HP motor
V-belt and pulley system
Vertical head
Kistler dynamometer
Locking set screw
Backing plate
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TrivexTM tool design

• 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

Side view of tool
Top view of probe
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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

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3 ipm 5 ipm 7 ipm 9 ipm 11 ipm 13 ipm
1000 rpm            
1500 rpm   x x x    
2000 rpm     x x x  
2100 rpm         x x
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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

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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
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1000 rpm, 10 ipm
0 in
9 in
18 in
27 in
36 in
1350 rpm, 10 ipm
0 in
9 in
36 in
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Reduction in probe diameter
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Reduction in probe length
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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 _at_ 10 ipm
1000 rpm _at_ 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 606120 Al2O3 MMC.
Materials Science and Engineering 349 (2003)
156-165.
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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

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Results MMC Weld Matrix using self-optimized
probe
3 ipm 5 ipm 7 ipm 9 ipm
500 rpm        
750 rpm        
1000 rpm x       
1250 rpm x  x     
1500 rpm   x     
defect
 
apparatus limit
 
 
defect free
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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

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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.

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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

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SEM images of coating
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Previous VUWAL results for smooth probe CVD-Moly
tool on Al-MMC
Travel speed (ipm) Percent decrease in axial force
4 9.2
6 10.4
8 12.6
10 effectively 0
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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

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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 35920 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 606120 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.

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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