Friction Stir Welding of Iron and Nickel Alloys

Transcription

1 Friction Stir Welding of Iron and Nickel Alloys Carl D. Sorensen Brigham Young University

2 Acknowledgements Tool materials and fabrication provided by Megastir Technologies, a business alliance between Smith International and Advanced Metal Products Welding and analysis provided by Russell Steel, Colin Sterling, and Yutaka Sato

3 Agenda Background Critical Technology Recent FSW Results in Fe and Ni alloys Potential Applications Getting Started

4 Friction Stir Welding Solid state joining process Rotating tool with small pin and large shoulder Frictional heating softens material Material flows around pin Shoulder consolidates material behind pin

5 Video Demonstration

6 FSW Advantages Reduced distortion, compared to fusion welds Stable, repeatable process Lower processing temperatures No melting, so no solidification defects Wrought, rather than cast, microstructure

7 FSW Applications Welding of deck plate for high-speed ferry Welding of extrusions for automotive parts Volvo seat back Ford steering link Welding of high-strength Al alloys Space shuttle Solid rocket motor Aircraft

8 FSW Limitations Relatively simple geometry Until recently, only materials with low melting temperatures Tool material must be significantly harder than workpiece at elevated temperature Now, materials with high melting temperatures are weldable Steel Stainless Steel Nickel-based Alloys

9 Potential FSW Joint Geometry Butt Joint Lap Joint Tee Joints Angle Joint

10 Critical Technology for HTM Superabrasive tool materials Composite tools Water-cooled, temperature and force sensing tool holder Computer-controlled machine Control based partially on tool load and tool temperature

11 Tool Materials PCBN Compound of B and N with diamond crystal structure Produced in high-temperature, ultra-high pressure press (1450 C, 870,000 psi) Outstanding material properties Second in hardness only to diamond Stable to 1200 C Chemically inert

12 Composite Tools WC Shank PCBN Insert High-strength locking collar Thermal barrier

13 Specialized Tool Holder Liquid cooling to protect machine spindle bearings Integrated thermocouple to measure tool temperature Integrated force sensor Axial tool load Lateral tool load

14 Computer-Controlled Controlled Machine 44 inch travel Force capacity 10,000 kgf Z, 5,000 kgf X Captures weld process data Measures tool temperature Can control position, velocity, or force

15 FSW of HSLA Steel

16 Recent FSW Results Alloy 1018 Steel 304 Stainless 2507 Super Duplex Alloy 201 Alloy 600 Alloy 718 Thickness in in in in in in. 40 CFH of Argon used in all welds 1 in. 0.6 in.

17 1018 Steel Consistent welds Outstanding tool life -- 80m (262 feet) 79 plunges much more than expected in production

18 1018 Tool Life

19 304 Stainless Large process window Outstanding mechanical properties Acceptable tool life 30 m (100 feet) Weld Parameters Rotation: 400 rev/min Travel: 3 in/min Load control: 9,000 lbf

20 304 Process Window 1300 Rotation speed (RPM) Travel speed (IPM) Preferentially etched region consists of only grain boundary attack. Preferentially etched region consists of both heavily etched regions and G.B. attack. There are holes at the advancing side of friction stir weld in the as-polished condition.

21 304 Microstructure Adv. Ret. Ret. Adv. Base material Base material (500x) Center of DXZ (500x)

22 Sigma Phase in x Sigma phase observed in bands Also observed at grain boundaries between bands 1000 x

23 304 Mechanical Properties 304 FSW Transverse Tensile Properties Sample Yield Strength 0.2 % offset KSI (MPa) Ultimate Tensile Strength KSI (MPa) Elongation % 400 RPM, 3 IPM Base Metal 51 (352) 55 (379) 95 (655) 98 (675) 54 56

24 304 Tensile Specimens

25 2507 Super Duplex Stainless Initial parameters only Rotation: 450 rev/min Travel: 3.5 in/min (88 mm/min) Load control: 7400 lbf

26 2507 Microstructure Ret. Adv. Base material (200x) Center of DXZ (200x)

27 2507 Phase Composition Ferrite : Red Austenite : Green Up1.5 Up1.5 R3 R1.5 0 A1.5 A3 R3 R1.5 0 A1.5 A3

28 2507 Mechanical Properties Sample 450 RPM, 3.5 IPM Base Metal Yield Strength 0.2 % offset KSI (MPa) 110 (762) 102 (705) 2507 FSW Transverse Tensile Properties Ultimate Tensile Strength KSI (MPa) 123 (845) 128 (886) Elongation % 19 30

29 Alloy 201 Weld Initial Parameters Rotation: 1000 rev/min Travel: 4 in/min (100 mm/min) 0.6 in. After 12 in. of weld Tool previously used in alloy 718

30 Alloy 201 Microstructure Adv. Ret. Base material (500x) TMAZ (50x) DXZ (500x)

31 Alloy 201 Mechanical Properties Ni 201 FSW Transverse Tensile Properties Sample Yield Strength 0.2 % offset KSI (MPa) Ultimate Tensile Strength KSI (MPa) Elongation % 1000 RPM, 4 IPM 28 (193) 65 (448) 34 Base Metal (from literature) 15 (103) 59 (406) 50

32 Alloy 600 Weld Initial Parameters Rotation: 450 rev/min Travel: 2.25 in/min (56 mm/min) After 6 feet of weld

33 Alloy 600 Microstructure Ret. Adv. Base material (100x) Center of Stir zone (100x)

34 Alloy 600 Mechanical Properties Alloy 600 FSW Transverse Tensile Properties Sample Yield Strength 0.2 % offset KSI (MPa) Ultimate Tensile Strength KSI (MPa) Elongation % 450RPM 2 ¼ IPM 54 (374) 104 (719) 27 Base Metal (annealed condition) 38 (263) 92 (631) 50

35 Alloy 718 Weld Initial Parameters Rotation: 500 rev/min Travel: 2 IPM 0.6 in. 0.6 in. After 4 feet of weld

36 Alloy 718 Microstructure Adv. Base material (500x) Center of DXZ (500x)

37 Alloy 718 Mechanical Properties Alloy 718 FSW Transverse Tensile Properties Sample Yield Strength 0.2 % offset KSI (MPa) Ultimate Tensile Strength KSI (MPa) Elongation % 500RPM, 2 IPM 97 (668) 143 (986) 16 Base Metal (Annealed, from literature) 67 (462) 130 (896) 41 Base Metal (precipitation hardened, from literature) 170 (1172) 202 (1392) 22

38 Achieving Success in FSW of Iron and Nickel Based Alloys Use standard technology PCBN tools Cooled, instrumented holder Data acquisition system Use standard practices Published in literature, conferences Available at MegaStir Workshop Optimize weld parameters Specific to material, thickness, joint geometry

39 Conclusion FSW is feasible as a commercial process for iron and nickel alloys Tool life has been as high as 80 meters, and is improving Mechanical properties of resulting welds are excellent All systems are in place to assure success