mechanical and metallurgical properties and forces of immersed friction stir welding of aa6061 t6
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Mechanical and Metallurgical Properties and Forces of Immersed Friction Stir Welding of AA6061-T6. Thomas Bloodworth Vanderbilt University. Overview. Introduction Theory and Objective VWAL Test Bed Experimental Setup Materials Testing Results and Conclusions Future Work. Introduction.

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mechanical and metallurgical properties and forces of immersed friction stir welding of aa6061 t6
Mechanical and Metallurgical Properties and Forces of Immersed Friction Stir Welding of AA6061-T6

Thomas Bloodworth

Vanderbilt University

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA

overview
Overview
  • Introduction
  • Theory and Objective
  • VWAL Test Bed
  • Experimental Setup
  • Materials Testing
  • Results and Conclusions
  • Future Work

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA

introduction
Introduction
  • Friction Stir Welding (FSW)
  • Frictional heat with sufficient axial (z) force plasticizes weld-piece (Thomas et al)
  • Advantageous to conventional welding techniques
  • Welds maintain up to 95% of UTS compared to parent material

Schematic of the FSW Process (Record JH, 2005)

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA

introduction4
Introduction
  • Light weight materials used in production (e.g. Aluminum)
  • FSW is used primarily to weld Aluminum Alloys (AA)
  • Process currently becoming more prevalent:
    • Aerospace (e.g. Boeing, Airbus)
    • Automotive (e.g. Audi)
    • Marine (SFSW / IFSW)

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA

objective
Objective
  • Submerged / Immersed FSW (SFSW / IFSW)
  • Joining of the weld piece completely submerged in a fluid (i.e. water)
  • Greater heat dissipation reduces grain size in the weld nugget (Hofmann and Vecchio)
    • Increases material hardness
    • Theoretically increases tensile strength

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA

objective6
Objective
  • Hofmann and Vecchio show decrease in grain size by an order of magnitude
  • Increase in weld quality in SFSW may lead to prevalent use in underwater repair and/or construction (Arbegast et al)
    • Friction Stir Spot Welds (FSSW)
    • Repair of faulty MIG welds (TWI)
  • Process must be quantitatively verified and understood before reliable uses may be attained

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA

slide7

VWAL Test Bed

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA

vwal capabilities
VWAL Capabilities
  • VUWAL Test Bed: Milwaukee #2K Universal Milling Machine utilizing a Kearney and Treker Heavy Duty Vertical Head Attachment modified to accommodate high spindle speeds.
  • 4 – axis position controlled automation
  • Experimental force and torque data recorded using a Kistler 4 – axis dynamometer (RCD) Type 9124 B
  • Rotational Speeds: 0 – 4000 rpm
  • Travel Speeds: 0 – 30 ipm

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA

vwal test bed
VWAL Test Bed
  • Anvil modified for a submerged welding environment
  • Water initially at room temperature
  • Equivalent welds run in air and water for mechanical comparison (i.e. Tensile testing, Cross Sectioning)

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA

experimental setup
Experimental Setup
  • Optimal dry welds run 2000 rpm, 16 ipm
  • Submerged welds speeds: 2000 – 3000 rpm, travel speeds 10 – 20 ipm
  • Weld samples
    • AA 6061-T6: 3 x 8 x ¼” (butt weld configuration)
  • Tool
    • 01PH Steel (Rockwell C38)
    • 5/8” non – profiled shoulder
    • ¼” – 20 tpi LH tool pin (probe) of length .235”
  • Clockwise rotation
  • Single pass welding

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA

experimental procedure
Experimental Procedure
  • Shoulder plunge and lead angle: .004” , 20
  • Fine adjustments in plunge depth have been noted to create significant changes in force data as well as excess flash buildup
  • Therefore, significant care and effort was put forth to ensure constant plunge depth of .004”
    • Vertical encoder accurate to 10 microns
  • Tool creeps into material from the side and run at constant velocity off the weld sample

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA

materials testing
Materials Testing
  • Tensile testing done using standards set using the AWS handbook
  • Samples milled for tensile testing
  • Tensile specimens were milled for each weld run
    • Nominal ½ “ wide x ¼ “ thick specimens were used for the testing

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA

slide13

Materials Testing

  • Tensile specimens tested using an Instron Universal Tester
  • Recorded values included UTS and UYS in lbf

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA

results
Results
  • Stress – Strain curves were generated from the data gathered from the tensile test
  • Weld pitch “rule” is not followed in IFSW (Revolutions / Inch)

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA

results15
Results

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA

cross section
Cross Section
  • Dry Weld Section (left)
  • IFSW (right)

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA

cross section17
Cross Section
  • Dry FSW 10x (left)
  • SFSW 50x (right)

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA

results18
Results

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA

results19
Results

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA

results20
Results

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA

conclusions
Conclusions
  • Submerged welds maintained 90-95% of parent UTS
  • Parent material UTS of 44.88 ksi compared well to the welded plate averaging UTS of ~41 ksi
  • Worm hole defect welds failed at 65% of parent UTS
    • effective dry weld equivalent tests not run
  • Optimal welds for IFSW required a weld pitch increase of 60%
  • Weld pitch of dry to wet optimal welds
    • Dry welds: wp = 2000/16 = 125 rev/inch
    • Wet welds: wp = 2000/10 = 200 rev/inch

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA

summary and conclusions
Summary and Conclusions
  • Average torque increased from FSW to IFSW
    • FSW: 16 Nm
    • SFSW: 18.5 Nm
  • Optimal submerged (wet) FSW’s were compared to conventional dry FSW
  • Decrease in grain growth in the weld nugget due to inhibition by the fluid (water)
  • Water welds performed as well if not better than dry welds in tensile tests

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA

acknowledgements
Acknowledgements
  • This work was supported in part by:
    • Los Alamos National Laboratory
    • NASA (GSRP and MSFC)
    • The American Welding Society
    • Robin Midgett for materials testing capabilities
    • UTSI for cross sectioning and microscopy

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA

future work
Future Work
  • Fracture Surface Microscopy
  • Hardness Testing for comparison
  • Further Mechanical testing
    • e.g. root bend tests

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA

references
References
  • Thomas M.W., Nicholas E.D., Needham J.C., Murch M.G., Templesmith P., Dawes C.J.:G.B. patent application No. 9125978.8, 1991.
  • Crawford R., Cook G.E. et al. “Robotic Friction Stir Welding”. Industrial Robot 2004 31 (1) 55-63.
  • Hofmann D.C. and Vecchio K.S. “Submerged friction stir processing (SFSP): An improved method for creating ultra-fine-grained bulk materials”. MS&E 2005.
  • Arbegast W. et al. “Friction Stir Spot Welding”. 6th International Symposium on FSW. 2006.

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA

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