Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA 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 1.Introduction 2.Theory and Objective 3.VWAL Test Bed 4.Experimental Setup 5.Materials Testing 6.Results and Conclusions 7.Future Work

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

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA 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 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 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 Shoulder plunge and lead angle:.004”, 2 0 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 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 Tensile specimens tested using an Instron Universal Tester Recorded values included UTS and UYS in lbf Materials Testing

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

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA Cross Section Dry Weld Section (left) IFSW (right)

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA Cross Section Dry FSW 10x (left) SFSW 50x (right)

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

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

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

Materials Science & Technology 2007; September 16-20, 2007 — Detroit, MI, USA Conclusions Submerged welds maintained 90-95% of parent UTS Parent material UTS of 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 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 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 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 Thomas M.W., Nicholas E.D., Needham J.C., Murch M.G., Templesmith P., Dawes C.J.:G.B. patent application No , Crawford R., Cook G.E. et al. “Robotic Friction Stir Welding”. Industrial Robot (1) Hofmann D.C. and Vecchio K.S. “Submerged friction stir processing (SFSP): An improved method for creating ultra-fine-grained bulk materials”. MS&E Arbegast W. et al. “Friction Stir Spot Welding”. 6 th International Symposium on FSW