Parameterization of Parameterization of Friction Stir Welding of Friction Stir Welding of

Al 6061/SiC/17.5p Al 6061/SiC/17.5p

Vanderbilt University Welding Automation Vanderbilt University Welding Automation LaboratoryLaboratory

Tracie PraterTracie PraterDr. George CookDr. George Cook

Dr. Al StraussDr. Al StraussDr. Jim DavidsonDr. Jim Davidson

Mick HowellMick Howell

Metal Matrix Composites Metal Matrix Composites (MMCs)(MMCs)

Composite material Composite material comprised of two parts:comprised of two parts:

1)1) Continuous metal Continuous metal matrixmatrix

2)2) Reinforcing particlesReinforcing particles Classification schemeClassification scheme• four digit numberfour digit number• type of reinforcementtype of reinforcement• percentage percentage

reinforcementreinforcement• form of reinforcement: form of reinforcement:

whiskers (w) or particles whiskers (w) or particles (p)(p)

Industrial applications of Al-Industrial applications of Al-MMCsMMCs

►Tank armorsTank armors►Structural components of aircraftStructural components of aircraft►Bicycle framesBicycle frames►Engine cylindersEngine cylinders

Previous work in fusion welding Previous work in fusion welding of Al-MMCsof Al-MMCs

Assessment of problems inherent in Assessment of problems inherent in welding MMCs using fusion welding MMCs using fusion techniques published by Storjohann, techniques published by Storjohann, et. al.et. al.

• compares GTA, EB, and LB with FSW compares GTA, EB, and LB with FSW welds of Aluminum alloy reinforced welds of Aluminum alloy reinforced with SiC whiskerswith SiC whiskers

• presence of deleterious presence of deleterious θθ phase phase (Al(Al44CC33) detected in all fusion-welded ) detected in all fusion-welded jointsjoints

• porosities in HAZporosities in HAZ• dissolution of SiC whiskers dissolution of SiC whiskers • can mitigate these effects through can mitigate these effects through

careful control of heat inputcareful 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?Why FSW?

► improved orientation improved orientation and shape of and shape of reinforcement in reinforcement in finished jointfinished joint

► lower temperature lower temperature process – absence of process – absence of meltingmelting

► repeatabilityrepeatability

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 Overall trends in FSW of MMCsMMCs

► severe tool wearsevere tool wear► upper limit of joint efficiencies in range of 60 to upper limit of joint efficiencies in range of 60 to

70 percent70 percent► changes in pre and post weld size and changes in pre and post weld size and

distribution of reinforcement particlesdistribution of reinforcement particles► weldability of a particular MMC is inversely weldability of a particular MMC is inversely

proportional to percentage reinforcementproportional to percentage reinforcement► narrow weld envelopenarrow 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 SetupExperimental Setup► Milwaukee #2K Universal Milling Machine modified for Milwaukee #2K Universal Milling Machine modified for

FSWFSW► 9 in x 3 in x ¼ in wide samples – butt weld configuration9 in x 3 in x ¼ in wide samples – butt weld configuration► clamping systemclamping system► tool rigidly mounted using locking set screwtool rigidly mounted using locking set screw► load and torque data recorded by Kistler rotating quartz load and torque data recorded by Kistler rotating quartz

4-component dynamometer4-component dynamometer► travel rate, rotation speed, plunge depth, and tool travel rate, rotation speed, plunge depth, and tool

position controlled through custom-built GUI position controlled through custom-built GUI

Kistler dynamometer

Backing plate

V-belt and pulley system

Vertical head

20 HP motor

Locking set screw

► Design developed by The Design developed by The Welding Institute (TWI) Welding Institute (TWI)

► Non-cylindrical smooth Non-cylindrical smooth probe which is nearly probe which is nearly triangular in shapetriangular in shape

► Research by TWI Research by TWI indicates Trivexindicates TrivexTMTM has has potential to reduce potential to reduce forces forces

► Probe measures .25” at Probe measures .25” at widest point and .235” in widest point and .235” in length; 3 degree taperlength; 3 degree taper

Side view of tool

Top view of probe

TrivexTrivexTMTM tool design tool design

Trivex results: non-reinforced Trivex results: non-reinforced Aluminum alloyAluminum alloy

►Data used as baseline for comparison Data used as baseline for comparison with metal matrix compositeswith metal matrix composites

►characterization of x, y, and z forces characterization of x, y, and z forces as function of rotation and travel as function of rotation and travel speed speed

►Tensile tests and microscopy used to Tensile tests and microscopy used to parameterize Trivex tool on parameterize Trivex tool on unreinforced Aluminum 6061unreinforced Aluminum 6061

Fx vs. Rotation speed for unreinforced Al alloy

-300

-250

-200

-150

-100

-50

0

50

100

150

200

1000 1500 2000 2100

Rotation speed

Fx

3 ipm

5 ipm

7 ipm

9 ipm

11 ipm

13 ipm

Fy vs. Rotation speed for Unreinforced Al alloy

-450

-400

-350

-300

-250

-200

-150

-100

-50

0

1000 1500 2000 2100

Rotation speed (rpm)

Fy

(N)

3 ipm

5 ipm

7 ipm

9 ipm

11 ipm

13 ipm

Fz vs. rotation speed for unreinforced Al alloy

0

1000

2000

3000

4000

5000

6000

7000

1000 1500 2000 2100

Rotation speed (rpm)

Fz

(N)

3 ipm

5 ipm

7 ipm

9 ipm

11 ipm

13 ipm

Torque vs. Rotation speed for unreinforced Al alloy

0

5

10

15

20

25

30

1000 1500 2000 2100

Rotation speed (rpm)

To

rqu

e (N

-m)

3 ipm

5 ipm

7 ipm

9 ipm

11 ipm

13 ipm

Peak load vs. rotation speed

0200400600800

100012001400160018002000

1000 1500 2000 2100

Rotation speed

Pea

k lo

ad (

kgf)

3 ipm

5 ipm

7 ipm

9 ipm

11 ipm

13 ipm

3 ipm3 ipm 5 ipm5 ipm 7 ipm7 ipm 9 ipm9 ipm 11 ipm11 ipm 13 ipm13 ipm

1000 1000 rpmrpm                  

1500 1500 rpmrpm    xx xx xx      

2000 2000 rpmrpm       xx xx xx   

2100 2100 rpmrpm             xx xx

Tool wear study on reinforced Al Tool wear study on reinforced Al alloyalloy

► 4 parameter sets chosen to assess influence 4 parameter sets chosen to assess influence of travel speed and rotation speed on wear of travel speed and rotation speed on wear raterate

• 1000 rpm, 4 ipm1000 rpm, 4 ipm• 1000 rpm, 10 ipm1000 rpm, 10 ipm• 1350 rpm, 4 ipm1350 rpm, 4 ipm• 1350 rpm, 10 ipm1350 rpm, 10 ipm Shadowgraph of each tool taken after every 9 Shadowgraph of each tool taken after every 9

inches of weldment; dimensions also recordedinches of weldment; dimensions also recorded

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

1000 rpm, 10 ipm

0 in

9 in

18 in 27 in 36 in

1350 rpm, 10 ipm

0 in

9 in

36 in

Reduction in probe diameterReduction in probe diameter

% Reduction in probe diameter vs. weld distance

0

2

4

6

8

10

12

14

16

18

0 in 9 in 18 in 27 in 36 in

Distance

% r

edu

ctio

n i

n d

iam

eter

1350 rpm @ 4 ipm

1000 rpm @ 4 ipm

1000 rpm @ 10 ipm

1350 rpm @ 10 ipm

Reduction in probe lengthReduction in probe length

% reduction in probe diameter vs. weld distance

0

0.5

1

1.5

2

2.5

3

3.5

4

0 in 9 in 18 in 27 in 36 in

Distance

% r

edu

ctio

n

1350_4

1000_4

1000_10

1350_10

Summary of wear resultsSummary of wear results

► Threshold beyond which no wear occurs (referred Threshold beyond which no wear occurs (referred to as the “self optimized shape”)to as the “self optimized shape”)33

► Welds with higher travel speeds result in less wearWelds with higher travel speeds result in less wear► Compromise which much be negotiated in joining Compromise which much be negotiated in joining

MMCs: welding speeds must be slow enough to MMCs: welding speeds must be slow enough to generate sufficient plastic deformation, yet fast generate sufficient plastic deformation, yet fast enough to mitigate severe tool wearenough 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 self-MMC Weld Matrix using self-optimized tooloptimized tool

► .009” plunge depth.009” plunge depth►1 degree tilt angle1 degree tilt angle►Rotation speeds: 500, 750, 1000, Rotation speeds: 500, 750, 1000,

1250, 1500 rpm1250, 1500 rpm►Travel rate: 3, 5, 7, 9 ipmTravel rate: 3, 5, 7, 9 ipm► Inconsistent load and torque data Inconsistent load and torque data

presumably due to misalignment presumably due to misalignment and/or gapping and/or gapping

Results: MMC Weld Matrix using Results: MMC Weld Matrix using self-optimized probeself-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”

Diamond Coating by Chemical Diamond Coating by Chemical Vapor Deposition (CVD)Vapor Deposition (CVD)

► Objective is to test CVD Objective is to test CVD as a means of creating as a means of creating superabrasive tools for superabrasive tools for welding of MMCswelding of MMCs

► Substrate is coated in Substrate is coated in plasma chamber plasma chamber containing methane containing methane and hydrogen gasand hydrogen gas

► Two activation Two activation reactions govern reactions govern coating processcoating process

► Same process used to Same process used to grow carbon nanotubesgrow carbon nanotubes

Diamond formation by CVDDiamond formation by CVD► Deryagin model of coating Deryagin model of coating

processprocess44

► Carbon coalesces on Carbon coalesces on substrate surface – substrate surface – transport rate of C is transport rate of C is reducedreduced

► Diamond nucleus is formed Diamond nucleus is formed when layer has grown to when layer has grown to critical sizecritical size

► Plasma increases reaction Plasma increases reaction raterate

4. Deryagin, B.V. and D.V. Fedosayev. “The Growth of 4. Deryagin, B.V. and D.V. Fedosayev. “The Growth of diamond and graphite from the gas phase.” diamond and graphite from the gas phase.” Surface Surface and Coatings Technologyand Coatings Technology 38 (1989): 131-248. 38 (1989): 131-248.

Tool designTool design

► Choice of material Choice of material dictated by dictated by environment of coating environment of coating chamberchamber

► Size of chamber also Size of chamber also necessitated two-part necessitated two-part tool designtool design

► Molybdenum probe and Molybdenum probe and shoulder manufactured shoulder manufactured by Midwest Tungsten of by Midwest Tungsten of Chicago, ILChicago, IL

► Press fit into 01 steel Press fit into 01 steel cylinder after coatingcylinder after coating

SEM images of coatingSEM images of coating

Previous VUWAL results for Previous VUWAL results for smooth probe CVD-Moly tool on smooth probe CVD-Moly tool on

Al-MMCAl-MMC

Travel speed (ipm)Travel speed (ipm)Percent decrease in axial Percent decrease in axial

forceforce

44 9.29.2

66 10.410.4

88 12.612.6

1010 effectively 0effectively 0

Future researchFuture research

►Comparison of tool wear and forces for Comparison of tool wear and forces for coated and uncoated Trivex tool in coated and uncoated Trivex tool in welding of MMCswelding of MMCs

►Tensile tests of MMC jointsTensile tests of MMC joints►RadiographyRadiography►Extend research to include other Extend research to include other

composite materialscomposite materials

ReferencesReferences1. 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 4. Deryagin, B.V. and D.V. Fedosayev. “The Growth of diamond and graphite from the gas phase.” graphite from the gas phase.” Surface and Coatings Surface and Coatings TechnologyTechnology 38 (1989): 131-248. 38 (1989): 131-248.

AcknowledgementsAcknowledgements

► UTSIUTSI► Vanderbilt University Machine ShopVanderbilt University Machine Shop► Vanderbilt University Diamond Fabrication LabVanderbilt University Diamond Fabrication Lab► sp3, Inc.sp3, Inc.► DWA CompositesDWA Composites► Midwest TungstenMidwest Tungsten► Drs. George Cook, Jim Davidson, Mick Howell, Drs. George Cook, Jim Davidson, Mick Howell,

Al Strauss, Tom Lienert, James Whitting Al Strauss, Tom Lienert, James Whitting