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
Metal Matrix Composites (MMCs)

1)
2)

•
•
•
•
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)
Industrial applications of Al-MMCs
► Tank
armors
► Structural components of aircraft
► Bicycle frames
► Engine cylinders
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.
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.
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.
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
20 HP
motor
V-belt and
pulley system
Kistler
dynamometer
Vertical
head
Locking
set screw
Backing
plate
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
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
Fx vs. Rotation speed for unreinforced Al alloy
200
150
100
3 ipm
Fx
50
0
-50
-100
5 ipm
1000
1500
2000
2100
7 ipm
9 ipm
11 ipm
-150
-200
13 ipm
-250
-300
Rotation speed
Fy vs. Rotation speed for Unreinforced Al alloy
0
Fy (N)
-50
1000
1500
2000
2100
-100
3 ipm
-150
5 ipm
-200
7 ipm
-250
9 ipm
-300
11 ipm
-350
13 ipm
-400
-450
Rotation speed (rpm)
Fz vs. rotation speed for unreinforced Al alloy
7000
Fz (N)
6000
3 ipm
5000
5 ipm
4000
7 ipm
3000
9 ipm
2000
11 ipm
13 ipm
1000
0
1000
1500
2000
Rotation speed (rpm)
2100
Torque vs. Rotation speed for unreinforced Al alloy
Torque (N-m)
30
25
3 ipm
20
5 ipm
7 ipm
15
9 ipm
10
11 ipm
5
13 ipm
0
1000
1500
2000
Rotation speed (rpm)
2100
Peak load (kgf)
Peak load vs. rotation speed
2000
1800
1600
1400
1200
1000
800
600
400
200
0
3 ipm
5 ipm
7 ipm
9 ipm
11 ipm
13 ipm
1000
1500
2000
2100
Rotation speed
3 ipm
5 ipm
7 ipm
9 ipm
x
x
x
x
x
11 ipm
13 ipm
1000 rpm
1500 rpm
2000 rpm
2100 rpm
x
x
x
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
1350 rpm, 4 ipm
0 in
9 in
0 in
9 in
18 in
27 in
36 in
27 in
36 in
1000 rpm, 4 ipm
18 in
1000 rpm, 10 ipm
0 in
9 in
0 in
9 in
18 in
1350 rpm, 10 ipm
36 in
27 in
36 in
Reduction in probe diameter
% reduction in diameter
% Reduction in probe diameter vs. weld distance
18
16
14
12
1350 rpm @ 4 ipm
10
8
1000 rpm @ 4 ipm
6
4
1350 rpm @ 10 ipm
1000 rpm @ 10 ipm
2
0
0 in
9 in
18 in
Distance
27 in
36 in
Reduction in probe length
% reduction in probe diameter vs. weld distance
4
% reduction
3.5
3
1350_4
2.5
1000_4
2
1000_10
1.5
1350_10
1
0.5
0
0 in
9 in
18 in
Distance
27 in
36 in
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.
MMC Weld Matrix using selfoptimized 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
Results: MMC Weld Matrix using selfoptimized probe
3 ipm
5 ipm
500 rpm
750 rpm
1000 rpm
x
1250 rpm
x
1500 rpm
x
x
defect
apparatus limit
“defect free”
7 ipm
9 ipm
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
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.
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
SEM images of coating
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
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
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.
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