Recent Developments in Friction Stir Welding Tools for Weld Bead Defects Minimization – A Review

Lader, Surendra Kumar; Baruah, Mayuri; Ballav, Raj; Bag, Swarup

doi:10.1590/0104-9224/SI28.06

Surendra Kumar Lader

investigation

methodology

writing-original draft

conceptualization

data curation

writing-reveiw & editing

formal analysis

National Institute of Technology, Production and Industrial Engineering Department, Jamshedpur, India.

http://orcid.org/0000-0001-8304-8920

Mayuri Baruah

conceptualization

writing-reveiw & editing

supervision

National Institute of Technology, Production and Industrial Engineering Department, Jamshedpur, India.

http://orcid.org/0000-0002-4689-4762

Raj Ballav

supervision

National Institute of Technology, Production and Industrial Engineering Department, Jamshedpur, India.

http://orcid.org/0000-0002-7520-8143

Swarup Bag

formal analysis

Indian Institute of Technology, Mechanical Engineering Department, Guwahati, India.

http://orcid.org/0000-0003-2553-831X

E-mails: surendralader@gmail.com (SKL), mayuri.prod@nitjsr.ac.in (MB), rballav.prod@nitjsr.ac.in (RB), swarupbag@iitg.ac.in (SB)

Figures (36)
Tables (10)

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Figure 1
FSW process.

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Figure 2
Classification of FSW conventional tools, advanced tools systems and FSW process parameters which affect the formation of weld flaws.

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Figure 3
Evolution of tool wear in the FSW of AA6061 with 01 AISI oil hardened tool steel at 1000 rpm rotational speed and welding speed of (a) 3 mm/sec (b) 9mm/sec: distances travelled by tool in meters are indicated in right below for each tool [³¹31 Prado RA, Murr LE, Soto KF, McClure JC. Self-optimization in tool wear for friction-stir welding of Al 6061+20% Al2O3 MMC. Materials Science and Engineering A. 2003;349(1-2):156-165. http://dx.doi.org/10.1016/S0921-5093(02)00750-5.
http://dx.doi.org/10.1016/S0921-5093(02)... ].

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Figure 4
Effect of tool coating on microstructure of AA7075-T651 for (a) uncoated tool (b) TiN coated tool at 900rpm tool rotational speed [³²32 Çevik B, Özçatalbas Y, Gulenc B. Effect of tool material on micro- Structure and mechanical properties in friction stir welding. Materials Testing. 2016;58(1):36-42. http://dx.doi.org/10.3139/120.110816.
http://dx.doi.org/10.3139/120.110816... ].

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Figure 5
Different types of FSW tool shoulder (a) and shoulder bottom surface features (b) [³⁹39 Wahid MA, Khan ZA, Siddiquee AN. Review on underwater friction stir welding: a variant of friction stir welding with great potential of improving joint properties. Transactions of Nonferrous Metals Society of China. 2018;28(2):193-219. http://dx.doi.org/10.1016/S1003-6326(18)64653-9.
http://dx.doi.org/10.1016/S1003-6326(18)... ].

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Figure 6
Tool geometry.

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Figure 7
Types of tool pin profiles used in FSW.

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Figure 8
Effect of tool rotational speed and welding speed in the development of weld joint for AA7075-T6 [⁷⁴74 Rajakumar S, Muralidharan C, Balasubramanian V. Influence of friction stir welding process and tool parameters on strength properties of AA7075-T6 aluminium alloy joints. Materials & Design. 2011;32(2):535-549. http://dx.doi.org/10.1016/j.matdes.2010.08.025.
http://dx.doi.org/10.1016/j.matdes.2010.... ].

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Figure 9
Cause and Effect Diagram (Fish Bone Diagram) for defect-less friction stir weld joints.

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Figure 10
SSFSW process schematic in 2D section view and 3D.

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Figure 11
Material flow pattern in the lap welding of AA2024-T6 alloy using traditional FSW (a) and (c), and NRSA-FSW (b) and (d) [¹¹⁶116 Ji S, Li Z, Zhou Z, Zhang L. Microstructure and mechanical property differences between friction stir lap welded joints using rotating and stationary shoulders. International Journal of Advanced Manufacturing Technology. 2017;90(9-12):3045-3053. http://dx.doi.org/10.1007/s00170-016-9640-y.
http://dx.doi.org/10.1007/s00170-016-964... ].

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Figure 12
AA2024–AA7050 weld cross-section: FSW at 600 rpm and different welding speeds (a) 180mm/min, (b) 300mm/min, (c) 480mm/min, and (d) NRSA-FSW at 1200 rpm and 180mm/min [¹¹⁹119 Barbini A, Carstensen J, dos Santos JF. Influence of a non-rotating shoulder on heat generation, microstructure and mechanical properties of dissimilar AA2024/AA7050 FSW joints. Journal of Materials Science and Technology. 2018;34(1):119-127. http://dx.doi.org/10.1016/j.jmst.2017.10.017.
http://dx.doi.org/10.1016/j.jmst.2017.10... ].

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Figure 13
Counter-rotating twin tool set-up (a) schematic diagram (b) [¹²⁵125 Kumari K, Pal SK, Singh SB. S. BratSingh, Friction stir welding by using counter-rotating twin tool. Journal of Materials Processing Technology. 2015;215:132-141. http://dx.doi.org/10.1016/j.jmatprotec.2014.07.031.
http://dx.doi.org/10.1016/j.jmatprotec.2... ].

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Figure 14
RDR-FSW (a) Schematic view and (b) Tool set-up image [¹³¹131 Li JQ, Liu HJ. Characteristics of the reverse dual-rotation friction stir welding conducted on 2219-T6 aluminum alloy. Materials & Design. 2013;45:148-154. http://dx.doi.org/10.1016/j.matdes.2012.08.068.
http://dx.doi.org/10.1016/j.matdes.2012.... ].

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Figure 15
Weld joint obtained from counter-rotating twin tool [¹²⁵125 Kumari K, Pal SK, Singh SB. S. BratSingh, Friction stir welding by using counter-rotating twin tool. Journal of Materials Processing Technology. 2015;215:132-141. http://dx.doi.org/10.1016/j.jmatprotec.2014.07.031.
http://dx.doi.org/10.1016/j.jmatprotec.2... ].

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Figure 16
Weld joint obtained from RDR-FSW [¹³²132 Liu HJ, Li JQ, Duan WJ. Research on reverse dual rotation friction stir welding process. Proceedings of the 1st International Joint Symposium on Joining and Weldin. 2013:25-32. http://dx.doi.org/10.1533/978-1-78242-164-1.25.
http://dx.doi.org/10.1533/978-1-78242-16... ].

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Figure 17
(a) AA2219-T6 weld macrograph of RDR-FSW (b) Macrograph of conventional FSW at 1800 rpm tool rotation and 200 mm/min welding speed.(AS: advancing side, RS: retreating side, BM: base metal, HAZ: heat affected zone, TMAZ: thermomechanically affected zone, SAZ: shoulder affected zone, WNZ: weld nugget zone) [¹³²132 Liu HJ, Li JQ, Duan WJ. Research on reverse dual rotation friction stir welding process. Proceedings of the 1st International Joint Symposium on Joining and Weldin. 2013:25-32. http://dx.doi.org/10.1533/978-1-78242-164-1.25.
http://dx.doi.org/10.1533/978-1-78242-16... ].

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Figure 18
Grain structures of AA2219-T6 weld nugget zone for conventional FSW and RDR-FSW at FSW at 800 rpm tool rotation, 200 mm/min welding speed (for both tool pin and assisted shoulder) and 0.2 mm plunge depth [¹³⁵135 Li JQ, Liu HJ. Effects of the reversely rotating assisted shoulder on microstructures during the reverse dual-rotation friction stir welding. Journal of Materials Science and Technology. 2015;31(4):375-383. http://dx.doi.org/10.1016/j.jmst.2014.07.020.
http://dx.doi.org/10.1016/j.jmst.2014.07... ].

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Figure 19
AA2219-T6 weld cross section of non-rotational shoulder assisted NRSA-FSW at constant 100 mm/min welding speed and different tool rotational speeds (a) 600 rpm, (b) 700 rpm, (c) 800 rpm, (d) 900 rpm, (e) 1000 rpm (abbreviations are mentioned in caption of ) [¹³⁶136 Li JQ, Liu HJ. Effects of tool rotation speed on microstructures and mechanical properties of AA2219-T6 welded by the external non-rotational shoulder assisted friction stir welding. Materials & Design. 2013;43:299-306. http://dx.doi.org/10.1016/j.matdes.2012.07.011.
http://dx.doi.org/10.1016/j.matdes.2012.... ].

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Figure 20
AA2219-T6 weld cross-section of RDR-FSW at 100 mm/min welding speed and 800 rpm rotational speed for both tool pin and reversely rotating shoulder (abbreviations are mentioned in caption of ) [¹³¹131 Li JQ, Liu HJ. Characteristics of the reverse dual-rotation friction stir welding conducted on 2219-T6 aluminum alloy. Materials & Design. 2013;45:148-154. http://dx.doi.org/10.1016/j.matdes.2012.08.068.
http://dx.doi.org/10.1016/j.matdes.2012.... ].

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Figure 21
Transmission electron microscopy (TEM) images of HAZ (a) Precipitates of conventional FSW, (b) Precipitates of RDR-FSW [¹³⁵135 Li JQ, Liu HJ. Effects of the reversely rotating assisted shoulder on microstructures during the reverse dual-rotation friction stir welding. Journal of Materials Science and Technology. 2015;31(4):375-383. http://dx.doi.org/10.1016/j.jmst.2014.07.020.
http://dx.doi.org/10.1016/j.jmst.2014.07... ].

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Figure 22
TEM images of precipitates at TMAZ (a) FSW joint (b) RDR-FSW joint [¹³⁵135 Li JQ, Liu HJ. Effects of the reversely rotating assisted shoulder on microstructures during the reverse dual-rotation friction stir welding. Journal of Materials Science and Technology. 2015;31(4):375-383. http://dx.doi.org/10.1016/j.jmst.2014.07.020.
http://dx.doi.org/10.1016/j.jmst.2014.07... ].

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Figure 23
AA7475-T7351 weld cross-section showing defects formation in conventional FSW(a, b) Lack of penetration at 300 rpm rotational speed (N) and 150 mm/min welding speed (V) [¹⁵⁶156 Tabatabaeipour M, Hettler J, Delrue S, Van Den Abeele K. NDT & E International Non-destructive ultrasonic examination of root defects in friction stir welded butt-joints. NDT & E International. 2016;80:23-34. http://dx.doi.org/10.1016/j.ndteint.2016.02.007.
http://dx.doi.org/10.1016/j.ndteint.2016... ] (c) Kissing bond at N of 500 rpm and V of 400 mm/min [¹⁵⁶156 Tabatabaeipour M, Hettler J, Delrue S, Van Den Abeele K. NDT & E International Non-destructive ultrasonic examination of root defects in friction stir welded butt-joints. NDT & E International. 2016;80:23-34. http://dx.doi.org/10.1016/j.ndteint.2016.02.007.
http://dx.doi.org/10.1016/j.ndteint.2016... ] (d) AA7085-T7452 weld cross-section showing tunnel, S-line and flash defect formation in Double Sided FSW at N of 950 rpm and V of 60 mm/min [¹⁵⁷157 Xu W, Wang H, Luo Y, Li W, Fu MW. Mechanical behavior of 7085-T7452 aluminum alloy thick plate joint produced by double-sided friction stir welding: effect of welding parameters and strain rates. Journal of Manufacturing Processes. 2018;35:261-270. http://dx.doi.org/10.1016/j.jmapro.2018.07.028.
http://dx.doi.org/10.1016/j.jmapro.2018.... ].

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Figure 24
SRFSW tool [¹⁶⁷167 Liu HJ, Hou JC, Guo H. Effect of welding speed on microstructure and mechanical properties of self-reacting friction stir welded 6061-T6 aluminum alloy. Materials & Design. 2013;50:872-878. http://dx.doi.org/10.1016/j.matdes.2013.03.105.
http://dx.doi.org/10.1016/j.matdes.2013.... ].

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Figure 25
Cylindrical 4 Flat (square) pin profile [¹⁶⁸168 Sued MK, Pons D, Lavroff J, Wong EH. Design features for bobbin friction stir welding tools: development of a conceptual model linking the underlying physics to the production process. Materials & Design. 2014;54:632-643. http://dx.doi.org/10.1016/j.matdes.2013.08.057.
http://dx.doi.org/10.1016/j.matdes.2013.... ].

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Figure 26
Schematic diagram of bobbin tool having the convex scrolled feature.

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Figure 27
Geometry of the bobbin tool having concave scrolled feature [¹⁶⁵165 Zhang H, Wang M, Zhang X, Yang G. Microstructural characteristics and mechanical properties of bobbin tool friction stir welded 2A14-T6 aluminum alloy. Materials & Design. 2015;65:559-566. http://dx.doi.org/10.1016/j.matdes.2014.09.068.].

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Figure 28
Macrographs of AA2A14-T6 showing formation of ellipse and triangular shaped region in the middle layer of NZ at constant 400 rpm tool rotation and at different welding speeds (V): (a) V=50 mm/min, (b) V=100 mm/min, (c) V=150 mm/min [¹⁶⁵165 Zhang H, Wang M, Zhang X, Yang G. Microstructural characteristics and mechanical properties of bobbin tool friction stir welded 2A14-T6 aluminum alloy. Materials & Design. 2015;65:559-566. http://dx.doi.org/10.1016/j.matdes.2014.09.068.].

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Figure 29
Schematic representation of material flow around SRFSW tool [¹⁷²172 Wan L, Huang Y, Guo W, Lv S, Feng J. Mechanical Properties and Microstructure of 6082-T6 Aluminum Alloy Joints by Self-support Friction Stir Welding. Journal of Materials Science and Technology. 2014;30(12):1243-1250. http://dx.doi.org/10.1016/j.jmst.2014.04.009.
http://dx.doi.org/10.1016/j.jmst.2014.04... ].

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Figure 30
AA6082-T6 macrographs of transverse cross-sections welded by Self-reacting tool at constant tool rotation of 800 rpm and welding speeds of (a)10 , (b) 50, (c) 100 and (d) 200mm/min (AS: advancing side, RS: retreating side, BM: base metal, HAZ: heat affected zone, TMAZ: thermomechanically affected zone) [¹⁷²172 Wan L, Huang Y, Guo W, Lv S, Feng J. Mechanical Properties and Microstructure of 6082-T6 Aluminum Alloy Joints by Self-support Friction Stir Welding. Journal of Materials Science and Technology. 2014;30(12):1243-1250. http://dx.doi.org/10.1016/j.jmst.2014.04.009.
http://dx.doi.org/10.1016/j.jmst.2014.04... ].

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Figure 31
Optical macrographs of AA2198-T851 for a) Conventional bobbin tool FSW (BT-FSW) and b) Dual rotation bobbin tool FSW (DBT-FSW). c) Typical void formation in BT-FSW. d) Advancing side of BT-FSW and e) DBT-FSW where USDZ is upper shoulder dominated zone and LSDZ is lower shoulder dominated zone (AS: advancing side, RS: retreating side, TMAZ: thermomechanically affected zone) [¹⁷³173 Wang FF, Li WY, Shen J, Wen Q. Improving weld formability by a novel dual-rotation bobbin toolfriction stir welding. Journal of Materials Science and Technology. 2017;1–5. http://dx.doi.org/10.1016/j.jmst.2017.11.001.
http://dx.doi.org/10.1016/j.jmst.2017.11... ].

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Figure 32
(a) IRFSW tool (b) Schematic illustrations of IRFSW tool, Rd is the rolling diameter of steel balls [¹⁸⁷187 Huang Y, Wan L, Lv S, Liu H, Feng J. Gradient micro-structured surface layer on aluminum alloy fabricated by in situ rolling friction stir welding. Materials & Design. 2013;52:821-827. http://dx.doi.org/10.1016/j.matdes.2013.06.026.
http://dx.doi.org/10.1016/j.matdes.2013.... ].

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Figure 33
Surface texture comparison of AAA2219 between conventional FSW and IRFSW processed samples at constant 600 rpm tool rotation and 300 mm/min welding speed (a) surface of conventional FSW samples (b) IRFSW with more than 0.05mm rolling depth (c) IRFSW with 0.05mm rolling depth (d) IRFSW with less than 0.05mm rolling depth [¹⁸⁷187 Huang Y, Wan L, Lv S, Liu H, Feng J. Gradient micro-structured surface layer on aluminum alloy fabricated by in situ rolling friction stir welding. Materials & Design. 2013;52:821-827. http://dx.doi.org/10.1016/j.matdes.2013.06.026.
http://dx.doi.org/10.1016/j.matdes.2013.... ].

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Figure 34
(a) Hardness and (b) Elastic Moduli comparison between base metal and IRFSW processed sample [¹⁸⁷187 Huang Y, Wan L, Lv S, Liu H, Feng J. Gradient micro-structured surface layer on aluminum alloy fabricated by in situ rolling friction stir welding. Materials & Design. 2013;52:821-827. http://dx.doi.org/10.1016/j.matdes.2013.06.026.
http://dx.doi.org/10.1016/j.matdes.2013.... ].

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Figure 35
AA2219 weld surface appearance of IRFSW at constant 600 rpm tool rotation and different welding speeds (a) IRFSW with high welding speed (500 mm/min) (b) IRFSW with optimized welding speed (300 mm/min) [¹⁰⁵105 Huang Y, Wan L, Lv S, Zhang J, Fu G. In situ rolling friction stir welding for joining AA2219. Materials & Design. 2013;50:810-816. http://dx.doi.org/10.1016/j.matdes.2013.03.088.
http://dx.doi.org/10.1016/j.matdes.2013.... ].

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Figure 36
Types of defects which can be rectified or eliminated with the various FSW assisted tool systems.

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Table 1
Common tool materials used for FSW of soft metals.

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Table 2
Influence of tool pin profile on the weld joint quality.

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Table 3
Defects obtained at various tool pin profiles and process parameters.

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Table 4
Remarkable effects of NRSA-FSW.

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Table 5
Insufficient and overheating defects.

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Table 6
Remarkable effects of CRTT-FSW.

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Table 7
Remarkable effects of RDR-FSW.

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Table 8
Remarkable effects of SRFSW.

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Table 9
Remarkable effects of IRFSW.

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Table 10
Effect of process parameters and tool pin profile on weld joint quality for various FSW assisted tool systems.

Tool Material	Work piece material
Mild Steel	Magnesium alloys
High Carbon Steel	Magnesium alloys
Armour Steel	Magnesium alloys
Stainless Steel	Magnesium alloys
AISI 4140	Dissimilar materials
AISI oil hardened tool steel	Aluminum matrix composite materials
High Speed Steel	Magnesium alloys
Tool Steel	Aluminum alloys, Dissimilar materials
H13 Steel	Magnesium alloys
SKD61 Tool Steel	Dissimilar materials
High Carbon High Chromium Steel	Magnesium alloys, Aluminum alloys, Dissimilar materials

Tool pin profile	Effect on weld joint quality
Straight Cylindrical Pin	Cracks and tunnel defects are formed due to lack of vertical displacement of material [⁴⁴44 Palanivel R, Koshy Mathews P, Murugan N, Dinaharan I. Effect of tool rotational speed and pin profile on microstructure and tensile strength of dissimilar friction stir welded AA5083-H111 and AA6351-T6 aluminum alloys. Materials & Design. 2012;40:7-16. http://dx.doi.org/10.1016/j.matdes.2012.03.027. http://dx.doi.org/10.1016/j.matdes.2012.... 45 Elangovan K, Balasubramanian V. Influences of pin profile and rotational speed of the tool on the formation of friction stir processing zone in AA2219 aluminium alloy. Materials Science and Engineering: A. 2007;459(1-2):7-18. http://dx.doi.org/10.1016/j.msea.2006.12.124. http://dx.doi.org/10.1016/j.msea.2006.12... 46 Elangovan K, Balasubramanian V. Influences of tool pin profile and welding speed on the formation of friction stir processing zone in AA2219 aluminium alloy. Journal of Materials Processing Technology. 2008;200(1-3):163-175. http://dx.doi.org/10.1016/j.jmatprotec.2007.09.019. http://dx.doi.org/10.1016/j.jmatprotec.2... -⁴⁷47 Padmanaban G, Balasubramanian V. Selection of FSW tool pin profile, shoulder diameter and material for joining AZ31B magnesium alloy - An experimental approach. Materials & Design. 2009;30(7):2647-2656. http://dx.doi.org/10.1016/j.matdes.2008.10.021. http://dx.doi.org/10.1016/j.matdes.2008.... ].
Tapered Cylindrical Pin	Insufficient flow of plasticized material due to low heat generation per unit weld length resulted in the formation of small pinholes and tunnel defect [⁴⁵45 Elangovan K, Balasubramanian V. Influences of pin profile and rotational speed of the tool on the formation of friction stir processing zone in AA2219 aluminium alloy. Materials Science and Engineering: A. 2007;459(1-2):7-18. http://dx.doi.org/10.1016/j.msea.2006.12.124. http://dx.doi.org/10.1016/j.msea.2006.12... 46 Elangovan K, Balasubramanian V. Influences of tool pin profile and welding speed on the formation of friction stir processing zone in AA2219 aluminium alloy. Journal of Materials Processing Technology. 2008;200(1-3):163-175. http://dx.doi.org/10.1016/j.jmatprotec.2007.09.019. http://dx.doi.org/10.1016/j.jmatprotec.2... -⁴⁷47 Padmanaban G, Balasubramanian V. Selection of FSW tool pin profile, shoulder diameter and material for joining AZ31B magnesium alloy - An experimental approach. Materials & Design. 2009;30(7):2647-2656. http://dx.doi.org/10.1016/j.matdes.2008.10.021. http://dx.doi.org/10.1016/j.matdes.2008.... ].
Threaded Cylindrical Pin	Threaded pin profile generates sufficient heat input and enhances the downward movement of plasticized material produces defect free weld [⁴⁵45 Elangovan K, Balasubramanian V. Influences of pin profile and rotational speed of the tool on the formation of friction stir processing zone in AA2219 aluminium alloy. Materials Science and Engineering: A. 2007;459(1-2):7-18. http://dx.doi.org/10.1016/j.msea.2006.12.124. http://dx.doi.org/10.1016/j.msea.2006.12... 46 Elangovan K, Balasubramanian V. Influences of tool pin profile and welding speed on the formation of friction stir processing zone in AA2219 aluminium alloy. Journal of Materials Processing Technology. 2008;200(1-3):163-175. http://dx.doi.org/10.1016/j.jmatprotec.2007.09.019. http://dx.doi.org/10.1016/j.jmatprotec.2... 47 Padmanaban G, Balasubramanian V. Selection of FSW tool pin profile, shoulder diameter and material for joining AZ31B magnesium alloy - An experimental approach. Materials & Design. 2009;30(7):2647-2656. http://dx.doi.org/10.1016/j.matdes.2008.10.021. http://dx.doi.org/10.1016/j.matdes.2008.... -⁴⁸48 Ilangovan M, Rajendra Boopathy S, Balasubramanian V. Effect of tool pin profile on microstructure and tensile properties of friction stir welded dissimilar AA 6061–AA 5086 aluminium alloy joints. Def. Technol. 2015;11(2):174-184. http://dx.doi.org/10.1016/j.dt.2015.01.004. http://dx.doi.org/10.1016/j.dt.2015.01.0... ].
Square Pin	Wider SZ formed due to large amount of material sweep from the SZ which resulted in turbulent flow of material and forms tunnel defect [⁴⁵45 Elangovan K, Balasubramanian V. Influences of pin profile and rotational speed of the tool on the formation of friction stir processing zone in AA2219 aluminium alloy. Materials Science and Engineering: A. 2007;459(1-2):7-18. http://dx.doi.org/10.1016/j.msea.2006.12.124. http://dx.doi.org/10.1016/j.msea.2006.12... 46 Elangovan K, Balasubramanian V. Influences of tool pin profile and welding speed on the formation of friction stir processing zone in AA2219 aluminium alloy. Journal of Materials Processing Technology. 2008;200(1-3):163-175. http://dx.doi.org/10.1016/j.jmatprotec.2007.09.019. http://dx.doi.org/10.1016/j.jmatprotec.2... -⁴⁷47 Padmanaban G, Balasubramanian V. Selection of FSW tool pin profile, shoulder diameter and material for joining AZ31B magnesium alloy - An experimental approach. Materials & Design. 2009;30(7):2647-2656. http://dx.doi.org/10.1016/j.matdes.2008.10.021. http://dx.doi.org/10.1016/j.matdes.2008.... ].
Triangular Pin	Abnormal stirring occurs due to insufficient heat input at the weld root resulted in the formation of cavity at the bottom of the weld joint [⁴⁵45 Elangovan K, Balasubramanian V. Influences of pin profile and rotational speed of the tool on the formation of friction stir processing zone in AA2219 aluminium alloy. Materials Science and Engineering: A. 2007;459(1-2):7-18. http://dx.doi.org/10.1016/j.msea.2006.12.124. http://dx.doi.org/10.1016/j.msea.2006.12... 46 Elangovan K, Balasubramanian V. Influences of tool pin profile and welding speed on the formation of friction stir processing zone in AA2219 aluminium alloy. Journal of Materials Processing Technology. 2008;200(1-3):163-175. http://dx.doi.org/10.1016/j.jmatprotec.2007.09.019. http://dx.doi.org/10.1016/j.jmatprotec.2... -⁴⁷47 Padmanaban G, Balasubramanian V. Selection of FSW tool pin profile, shoulder diameter and material for joining AZ31B magnesium alloy - An experimental approach. Materials & Design. 2009;30(7):2647-2656. http://dx.doi.org/10.1016/j.matdes.2008.10.021. http://dx.doi.org/10.1016/j.matdes.2008.... ].
Square Frustum Pin	Uniform mixing at the weld region [⁴⁹49 Jamshidi Aval H. Influences of pin profile on the mechanical and microstructural behaviors in dissimilar friction stir welded AA6082-AA7075 butt Joint. Materials & Design. 2015;67:413-421. http://dx.doi.org/10.1016/j.matdes.2014.11.055. http://dx.doi.org/10.1016/j.matdes.2014.... ]
Fluted Ridge Groove Pin	Offers good weld symmetry and reduces the grain size which improves the strength of the weld joint [⁵⁰50 Akinlabi ET. Effect of shoulder size on weld properties of dissimilar metal friction stir welds. Journal of Materials Engineering and Performance. 2012;21(7):1514-1519. http://dx.doi.org/10.1007/s11665-011-0046-6. http://dx.doi.org/10.1007/s11665-011-004... 51 Thomas WM, Johnson KI, Wiesner CS. Friction stir welding-recent developments in tool and process technologies. Advanced Engineering Materials. 2003;5(7):485-490. http://dx.doi.org/10.1002/adem.200300355. http://dx.doi.org/10.1002/adem.200300355... -⁵²52 Srinivasa Rao MS, Ravi Kumar BVR, Manzoor Hussain M. Experimental study on the effect of welding parameters and tool pin profiles on the IS:65032 aluminum alloy FSW joints. Materials Today: Proceedings. 2017;4(2):1394-1404. http://dx.doi.org/10.1016/j.matpr.2017.01.161. http://dx.doi.org/10.1016/j.matpr.2017.0... ]
Fluted Pin	Improper stirring and tool jamming occurs resulted in the formation of tunnel defect [⁵³53 Azizieh M, Kokabi AH, Abachi P. Effect of rotational speed and probe profile on microstructure and hardness of AZ31/Al2O3 nanocomposites fabricated by friction stir processing. Materials & Design. 2011;32(4):2034-2041. http://dx.doi.org/10.1016/j.matdes.2010.11.055. http://dx.doi.org/10.1016/j.matdes.2010.... ].

Authors, Tool Pin Geometry	Process Parameters	Type of defect and its cause
Pin geometry: Straight cylindrical - I
Padmanaban and Balasubramanian [⁴⁷47 Padmanaban G, Balasubramanian V. Selection of FSW tool pin profile, shoulder diameter and material for joining AZ31B magnesium alloy - An experimental approach. Materials & Design. 2009;30(7):2647-2656. http://dx.doi.org/10.1016/j.matdes.2008.10.021. http://dx.doi.org/10.1016/j.matdes.2008.... ]	N: 1600	Fig. I - A [⁴⁷47 Padmanaban G, Balasubramanian V. Selection of FSW tool pin profile, shoulder diameter and material for joining AZ31B magnesium alloy - An experimental approach. Materials & Design. 2009;30(7):2647-2656. http://dx.doi.org/10.1016/j.matdes.2008.10.021. http://dx.doi.org/10.1016/j.matdes.2008.... ]
PD: 6	V: 40	Crack defect formed due to Lack of vertical displacement of material.
PD: 6	Z: 0.2
PL: 5.7	T: 00
PL: 5.7	F: 3
Elangovan and Balasubramanian [⁴⁶46 Elangovan K, Balasubramanian V. Influences of tool pin profile and welding speed on the formation of friction stir processing zone in AA2219 aluminium alloy. Journal of Materials Processing Technology. 2008;200(1-3):163-175. http://dx.doi.org/10.1016/j.jmatprotec.2007.09.019. http://dx.doi.org/10.1016/j.jmatprotec.2... ]	N: 1600	Fig. I - B [⁴⁶46 Elangovan K, Balasubramanian V. Influences of tool pin profile and welding speed on the formation of friction stir processing zone in AA2219 aluminium alloy. Journal of Materials Processing Technology. 2008;200(1-3):163-175. http://dx.doi.org/10.1016/j.jmatprotec.2007.09.019. http://dx.doi.org/10.1016/j.jmatprotec.2... ]
	V:
PD: 6	a) 22	(a, b) Tunnel defects and pin holes are formed in the weld root towards the retreating side of the weld joint due to improper stirring of the tool pin. (c) Large tunnel defect was formed due to insufficient heat input.
	b) 45
	c) 75
PL: 5.7	Z: NA
	T: NA
	F: 12
Elangovan and Balasubramanian [⁴⁵45 Elangovan K, Balasubramanian V. Influences of pin profile and rotational speed of the tool on the formation of friction stir processing zone in AA2219 aluminium alloy. Materials Science and Engineering: A. 2007;459(1-2):7-18. http://dx.doi.org/10.1016/j.msea.2006.12.124. http://dx.doi.org/10.1016/j.msea.2006.12... ]	N:	Fig. I - C [⁴⁵45 Elangovan K, Balasubramanian V. Influences of pin profile and rotational speed of the tool on the formation of friction stir processing zone in AA2219 aluminium alloy. Materials Science and Engineering: A. 2007;459(1-2):7-18. http://dx.doi.org/10.1016/j.msea.2006.12.124. http://dx.doi.org/10.1016/j.msea.2006.12... ]
	a) 1500
PD: 6	b) 1600	(a, b) Tunnel defects are formed at the root of the weld joint due to insufficient heat input. (c) Pin holes due to improper flow of the plasticized material.
	c) 1700
	V: 45
PL: 5.7	Z: 0.2
	T: 00
	F: 12
Pin geometry: Tapered cylindrical - II
Padmanaban and Balasubramanian [⁴⁷47 Padmanaban G, Balasubramanian V. Selection of FSW tool pin profile, shoulder diameter and material for joining AZ31B magnesium alloy - An experimental approach. Materials & Design. 2009;30(7):2647-2656. http://dx.doi.org/10.1016/j.matdes.2008.10.021. http://dx.doi.org/10.1016/j.matdes.2008.... ]	N: 1600	Fig. II - A [⁴⁷47 Padmanaban G, Balasubramanian V. Selection of FSW tool pin profile, shoulder diameter and material for joining AZ31B magnesium alloy - An experimental approach. Materials & Design. 2009;30(7):2647-2656. http://dx.doi.org/10.1016/j.matdes.2008.10.021. http://dx.doi.org/10.1016/j.matdes.2008.... ]
PD: 6 (root)	V: 40	A long crack formed due to the absence of vertical motion of the material.
PL: 5.7	Z: 0.2
	T: 00
	F: 3
Elangovan and Balasubramanian [⁴⁶46 Elangovan K, Balasubramanian V. Influences of tool pin profile and welding speed on the formation of friction stir processing zone in AA2219 aluminium alloy. Journal of Materials Processing Technology. 2008;200(1-3):163-175. http://dx.doi.org/10.1016/j.jmatprotec.2007.09.019. http://dx.doi.org/10.1016/j.jmatprotec.2... ]	N: 1600	Fig. II - B [⁴⁶46 Elangovan K, Balasubramanian V. Influences of tool pin profile and welding speed on the formation of friction stir processing zone in AA2219 aluminium alloy. Journal of Materials Processing Technology. 2008;200(1-3):163-175. http://dx.doi.org/10.1016/j.jmatprotec.2007.09.019. http://dx.doi.org/10.1016/j.jmatprotec.2... ]
	V:
PD: 6	a) 22	(a, b) Small pinholes are formed at the bottom of the weld joint because of insufficient flow of plasticized material. (c) Tunnel defect was formed due to low heat generation per unit weld length.
	b) 45
	c) 75
PL: 5.7	Z: NA
	T: NA
	F: 12
Elangovan and Balasubramanian [⁴⁵45 Elangovan K, Balasubramanian V. Influences of pin profile and rotational speed of the tool on the formation of friction stir processing zone in AA2219 aluminium alloy. Materials Science and Engineering: A. 2007;459(1-2):7-18. http://dx.doi.org/10.1016/j.msea.2006.12.124. http://dx.doi.org/10.1016/j.msea.2006.12... ]	N:	Fig. II - C [⁴⁵45 Elangovan K, Balasubramanian V. Influences of pin profile and rotational speed of the tool on the formation of friction stir processing zone in AA2219 aluminium alloy. Materials Science and Engineering: A. 2007;459(1-2):7-18. http://dx.doi.org/10.1016/j.msea.2006.12.124. http://dx.doi.org/10.1016/j.msea.2006.12... ]
	a) 1500
PD: 6	b) 1600	(a, c) Tunnel defect due to insufficient heat input. (b) Pin holes are formed since there is absence of vertical flow of material.
	c) 1700
	V: 45
PL: 5.7	Z: 0.2
	T: 00
	F: 12
Pin geometry: Threaded cylindrical - III
Padmanaban and Balasubramanian [⁴⁷47 Padmanaban G, Balasubramanian V. Selection of FSW tool pin profile, shoulder diameter and material for joining AZ31B magnesium alloy - An experimental approach. Materials & Design. 2009;30(7):2647-2656. http://dx.doi.org/10.1016/j.matdes.2008.10.021. http://dx.doi.org/10.1016/j.matdes.2008.... ]	N: 1600	Fig. III - A [⁴⁷47 Padmanaban G, Balasubramanian V. Selection of FSW tool pin profile, shoulder diameter and material for joining AZ31B magnesium alloy - An experimental approach. Materials & Design. 2009;30(7):2647-2656. http://dx.doi.org/10.1016/j.matdes.2008.10.021. http://dx.doi.org/10.1016/j.matdes.2008.... ]
PD: 6	V: 40	Defect-free joints are formed due to sufficient heat generation and proper mixing of materials.
PL: 5.7	Z: 0.2
	T: 00
	F: 3
Elangovan and Balasubramanian [⁴⁶46 Elangovan K, Balasubramanian V. Influences of tool pin profile and welding speed on the formation of friction stir processing zone in AA2219 aluminium alloy. Journal of Materials Processing Technology. 2008;200(1-3):163-175. http://dx.doi.org/10.1016/j.jmatprotec.2007.09.019. http://dx.doi.org/10.1016/j.jmatprotec.2... ]	N: 1600	Fig. III - B [⁴⁶46 Elangovan K, Balasubramanian V. Influences of tool pin profile and welding speed on the formation of friction stir processing zone in AA2219 aluminium alloy. Journal of Materials Processing Technology. 2008;200(1-3):163-175. http://dx.doi.org/10.1016/j.jmatprotec.2007.09.019. http://dx.doi.org/10.1016/j.jmatprotec.2... ]
	V:
PD: 6	a) 22	(a) Crack-like defect formed due to excess heat input results in turbulent material flow. (b) Defect-free joint due to sufficient heat input. (c) Tunnel defect formed at the middle of the stirred zone due to faster welding speed results in lower heat input.
	b) 45
	c) 75
PL: 5.7	Z: NA
	T: NA
	F: 12
Elangovan and Balasubramanian [⁴⁵45 Elangovan K, Balasubramanian V. Influences of pin profile and rotational speed of the tool on the formation of friction stir processing zone in AA2219 aluminium alloy. Materials Science and Engineering: A. 2007;459(1-2):7-18. http://dx.doi.org/10.1016/j.msea.2006.12.124. http://dx.doi.org/10.1016/j.msea.2006.12... ]	N:	Fig. III - C [⁴⁵45 Elangovan K, Balasubramanian V. Influences of pin profile and rotational speed of the tool on the formation of friction stir processing zone in AA2219 aluminium alloy. Materials Science and Engineering: A. 2007;459(1-2):7-18. http://dx.doi.org/10.1016/j.msea.2006.12.124. http://dx.doi.org/10.1016/j.msea.2006.12... ]
	a) 1500
PD: 6	b) 1600	(a, b) No defect because the threaded pin profile generates sufficient heat input and enhances the downward movement of plasticized material. (c) Pin holes are formed because of excess turbulent flow of materials takes place at higher tool rotational speed.
	c) 1700
	V: 45
PL: 5.7	Z: 0.2
	T: 00
	F: 12
Pin geometry: Square - IV
Padmanaban and Balasubramanian [⁴⁷47 Padmanaban G, Balasubramanian V. Selection of FSW tool pin profile, shoulder diameter and material for joining AZ31B magnesium alloy - An experimental approach. Materials & Design. 2009;30(7):2647-2656. http://dx.doi.org/10.1016/j.matdes.2008.10.021. http://dx.doi.org/10.1016/j.matdes.2008.... ]	N: 1600	Fig. IV - A [⁴⁷47 Padmanaban G, Balasubramanian V. Selection of FSW tool pin profile, shoulder diameter and material for joining AZ31B magnesium alloy - An experimental approach. Materials & Design. 2009;30(7):2647-2656. http://dx.doi.org/10.1016/j.matdes.2008.10.021. http://dx.doi.org/10.1016/j.matdes.2008.... ]
PD: NA	V: 40	Tunnel defect formed due to large amount of material sweep from the SZ.
PL: 5.7	Z: 0.2
	T: 00
	F: 3
Elangovan and Balasubramanian [⁴⁶46 Elangovan K, Balasubramanian V. Influences of tool pin profile and welding speed on the formation of friction stir processing zone in AA2219 aluminium alloy. Journal of Materials Processing Technology. 2008;200(1-3):163-175. http://dx.doi.org/10.1016/j.jmatprotec.2007.09.019. http://dx.doi.org/10.1016/j.jmatprotec.2... ]	N: 1600	Fig. IV - B [⁴⁶46 Elangovan K, Balasubramanian V. Influences of tool pin profile and welding speed on the formation of friction stir processing zone in AA2219 aluminium alloy. Journal of Materials Processing Technology. 2008;200(1-3):163-175. http://dx.doi.org/10.1016/j.jmatprotec.2007.09.019. http://dx.doi.org/10.1016/j.jmatprotec.2... ]
	V:
PD: NA	a) 22	(a) Defect-free weld joint. A wider weld zone appeared due to excess heat input at a higher rotational speed. (b) Defect-free joint and adequate heat input. (c) Defect-free joint. A narrower weld zone appeared due to low heat input at lower tool rotational speed.
	b) 45
	c) 75
PL: 5.7	Z: NA
	T: NA
	F: 12
Elangovan and Balasubramanian [⁴⁵45 Elangovan K, Balasubramanian V. Influences of pin profile and rotational speed of the tool on the formation of friction stir processing zone in AA2219 aluminium alloy. Materials Science and Engineering: A. 2007;459(1-2):7-18. http://dx.doi.org/10.1016/j.msea.2006.12.124. http://dx.doi.org/10.1016/j.msea.2006.12... ]	N:	Fig. IV - C [⁴⁵45 Elangovan K, Balasubramanian V. Influences of pin profile and rotational speed of the tool on the formation of friction stir processing zone in AA2219 aluminium alloy. Materials Science and Engineering: A. 2007;459(1-2):7-18. http://dx.doi.org/10.1016/j.msea.2006.12.124. http://dx.doi.org/10.1016/j.msea.2006.12... ]
	a) 1500
PD: NA	b) 1600	(a) and (b) Defect-free joint. Adequate heat input and sufficient working of plasticized metal. (c) Defect-free joint. A wider weld zone appeared due to excess working of plasticized metal at higher tool rotational speed.
	c) 1700
	V: 45
PL: 5.7	Z: 0.2
	T: 00
	F: 12
Pin geometry: Traingular - V
Padmanaban and Balasubramanian [⁴⁷47 Padmanaban G, Balasubramanian V. Selection of FSW tool pin profile, shoulder diameter and material for joining AZ31B magnesium alloy - An experimental approach. Materials & Design. 2009;30(7):2647-2656. http://dx.doi.org/10.1016/j.matdes.2008.10.021. http://dx.doi.org/10.1016/j.matdes.2008.... ]	N: 1600	Fig. V - A [⁴⁷47 Padmanaban G, Balasubramanian V. Selection of FSW tool pin profile, shoulder diameter and material for joining AZ31B magnesium alloy - An experimental approach. Materials & Design. 2009;30(7):2647-2656. http://dx.doi.org/10.1016/j.matdes.2008.10.021. http://dx.doi.org/10.1016/j.matdes.2008.... ]
PD: NA	V: 40	A cavity at the weld root appeared due to insufficient heat input.
PL: 5.7	Z: 0.2
	T: 00
	F: 3
Elangovan and Balasubramanian [⁴⁶46 Elangovan K, Balasubramanian V. Influences of tool pin profile and welding speed on the formation of friction stir processing zone in AA2219 aluminium alloy. Journal of Materials Processing Technology. 2008;200(1-3):163-175. http://dx.doi.org/10.1016/j.jmatprotec.2007.09.019. http://dx.doi.org/10.1016/j.jmatprotec.2... ]	N: 1600	Fig. V - B [⁴⁶46 Elangovan K, Balasubramanian V. Influences of tool pin profile and welding speed on the formation of friction stir processing zone in AA2219 aluminium alloy. Journal of Materials Processing Technology. 2008;200(1-3):163-175. http://dx.doi.org/10.1016/j.jmatprotec.2007.09.019. http://dx.doi.org/10.1016/j.jmatprotec.2... ]
	V:
PD: NA	a) 22	(a) Formation of tunnel defect due to excess turbulence of the plasticized metal at higher tool rotational speed. (b) Defect-free joint. Adequate heat input and sufficient working of plasticized metal. (c) Abnormal stirring of the tool pin causes a bigger tunnel defect at the weld root towards the retreating side.
	b) 45
	c) 75
PL: 5.7	Z: NA
	T: NA
	F: 12
Elangovan and Balasubramanian[⁴⁵45 Elangovan K, Balasubramanian V. Influences of pin profile and rotational speed of the tool on the formation of friction stir processing zone in AA2219 aluminium alloy. Materials Science and Engineering: A. 2007;459(1-2):7-18. http://dx.doi.org/10.1016/j.msea.2006.12.124. http://dx.doi.org/10.1016/j.msea.2006.12... ]	N:	Fig. V - C [⁴⁵45 Elangovan K, Balasubramanian V. Influences of pin profile and rotational speed of the tool on the formation of friction stir processing zone in AA2219 aluminium alloy. Materials Science and Engineering: A. 2007;459(1-2):7-18. http://dx.doi.org/10.1016/j.msea.2006.12.124. http://dx.doi.org/10.1016/j.msea.2006.12... ]
	a) 1500
PD: NA	b) 1600	(a) Pin holes are formed towards the retreating side due to insufficient heat input. (b) Defect-free joint. Adequate heat input and sufficient working of plasticized metal. (c) Defect-free joint. Adequate heat input and sufficient working of plasticized metal.
	c) 1700
	V: 45
PL: 5.7	Z: 0.2
	T: 00
	F: 12

Authors	NRSA-FSW tool geometry	FSW process parameters	Remarkable effects of NRSA-FSW
Alloy, Tool Material	a) NRS-OD/ID
	b) RTS-SD/PTD/PBD/PL
	c) PP
Li et al. [¹²¹121 Li JQ, Liu HJ. Design of tool system for the external nonrotational shoulder assisted friction stir welding and its experimental validations on 2219-T6 aluminum alloy. International Journal of Advanced Manufacturing Technology. 2013;66(5-8):623-634. http://dx.doi.org/10.1007/s00170-012-4353-3. http://dx.doi.org/10.1007/s00170-012-435... ]
AA2219-T6	a) 14/10	N_P: 600-800	1. Improve tensile strength, due to the violent material flow in the SZ and broadens process parameter range.
H: 5	b) 9.8/NA/NA/4.8	V: 100
TM: NA	c) PP: Conical threaded pin	Z: 0.2
		T: NA
		F: NA
Avettand-Fènoël and Taillard [¹¹²112 Avettand-Fènoël MN, Taillard R. Effect of a pre or postweld heat treatment on microstructure and mechanical properties of an AA2050 weld obtained by SSFSW. Materials & Design. 2016;89:348-361. http://dx.doi.org/10.1016/j.matdes.2015.09.151. http://dx.doi.org/10.1016/j.matdes.2015.... ]			1. Grain refinement occurs in post-aged heat treated samples as compared to pre-aged base metals.
AA2050-T3	a) 21.5/NA	N_P: 400	2. Joint efficiency shows no effect of aging sequence
H: 15	b) NA/10/NA/10	V: 100
TM: NA	c) PP: Truncated with thread having flute	Z: NA
		T: NA
		F: NA
You et al. [¹¹⁰110 You J, Zhao Y, Dong C, Wang C, Miao S, Yi Y, et al. Microstructure characteristics and mechanical properties of stationary shoulder friction stir welded 2219-T6 aluminium alloy at high rotation speeds. International Journal of Advanced Manufacturing Technology. 2020;108(4):987-996. http://dx.doi.org/10.1007/s00170-019-04594-1. http://dx.doi.org/10.1007/s00170-019-045... ]
AA2219-T6	a) 14/8	N_P: 2000-2600	1. Welding torque significantly reduces by increasing welding speed, which is highly suited for robotic manufacturing.
H: 4	b) 8/5/4/3.9	V: 100	2.Enhanced mixing of materials occurs in the SZ by increasing tool rotational speeds
TM: NA	c) PP: Conical threaded pin	Z: NA
		T: NA
		F: NA
Ji et al. [¹¹¹111 Ji SD, Meng XC, Liu JG, Zhang LG, Gao SS. Formation and mechanical properties of stationary shoulder friction stir welded 6005A-T6 aluminum alloy. Materials & Design. 2014;62:113-117. http://dx.doi.org/10.1016/j.matdes.2014.05.016. http://dx.doi.org/10.1016/j.matdes.2014.... ]
AA6005-T6	a) 12/6.3	N_P: 2000	1. Obtained defect-less joints with smooth weld surface.
H: 4	b) 6/5/NA/3	V: 100-600
TM: NA	c) PP: Tapered threaded pin	Z: NA
		T: NA
		F: NA
Li et al. [¹¹³113 Li D, Yang X, Cui L, He F, Shen H. Effect of welding parameters on microstructure and mechanical properties of AA6061-T6 butt welded joints by stationary shoulder friction stir welding. Materials & Design. 2014;64:251-260. http://dx.doi.org/10.1016/j.matdes.2014.07.046. http://dx.doi.org/10.1016/j.matdes.2014.... ]
AA6061-T6	a) 16/NA	N_P: 750-1500	1. No visible TMAZ and narrower HAZ.
H: 5	b) NA/8/5/4.9	V: 100-300
TM: NA	c) PP: Conical threaded pin	Z: NA
		T: NA
		F: NA
Li et al. [¹²²122 Li Z, Yue Y, Ji S, Chai P, Zhou Z. Joint features and mechanical properties of friction stir lap welded alclad 2024 aluminum alloy assisted by external stationary shoulder. Materials & Design. 2016;90:238-247. http://dx.doi.org/10.1016/j.matdes.2015.10.056. http://dx.doi.org/10.1016/j.matdes.2015.... ]
AA2024-T4	a) 17/10.5	N_P: 800-1200	1. High rotational speed is required for the adequate vertical displacement of the material in the SZ.
H: 3	b) 10/5/3.5/5	V: 50
TM: NA	c) PP: Tapered threaded pin	Z: 0.2
		T: NA
		F: NA
Yue et al. [¹¹⁵115 Yue Y, Zhou Z, Ji S, Zhang J, Li Z. Effect of welding speed on joint feature and mechanical properties of friction stir lap welding assisted by external stationary shoulders. International Journal of Advanced Manufacturing Technology. 2017;89(5-8):1691-1698. http://dx.doi.org/10.1007/s00170-016-9240-x. http://dx.doi.org/10.1007/s00170-016-924... ]
AA2024-T4	a) 17,21/10.5	N_P: 1000	1. High welding speed leads to void formation on the advancing side.
H: 3	b) 10/5/3.5/5	V: 50-200	2. Increase in the diameter of stationary shoulder increases effective sheet thickness and effective lap width.
TM: NA	c) PP: Tapered threaded pin	Z: 0.2
		T: NA
		F: NA
Buffa et al. [¹²³123 Buffa G, Fratini L, Impero F, Masnata A, Scherillo F, Squillace A. Surface and mechanical characterization of stationary shoulder friction stir welded lap joints: experimental and numerical approach. International Journal of Material Forming. 2020;13(5):725-736. http://dx.doi.org/10.1007/s12289-020-01574-9. http://dx.doi.org/10.1007/s12289-020-015... ]
AA6082-T6	a) 9/NA	N_P: 2500	1. Obtained high quality surface with no flash defects.
H: 2	b) NA/3/NA/3	V: 480	2. Temperature distribution was found consistent due to stationary shoulder.
TM: NA	c) PP: Conical threaded pin	Z: NA
		T: NA
		F: NA
Chen et al. [¹¹⁴114 Chen Y, Li H, Wang X, Ding H, Zhang F. A comparative investigation on conventional and stationary shoulder friction stir welding of Al-7075 butt-lap structure. Metals. 2019;9(12):1264. http://dx.doi.org/10.3390/met9121264. http://dx.doi.org/10.3390/met9121264... ]	a) 11/NA	N_P: 1200	1. As compared to traditional FSW, hook defect was eliminated in the joints produced by stationary shoulder.
AA7075-T651	b) NA/5/4/2.75	V: 200	2. Low heat input prevents the coarsening of strengthening precipitates and fracture took place from the zone of kissing bond defect.
H: 5-3	c) PP: NA	Z: 0.25
TM: NA		T: NA
		F: NA

Heat input	Type of defect	Material and Process parameter
Insufficient heat input	Cavity defect	1) Material: ADC12
		2) N: 1500
		3) V: 500
		4) F: 6.9
Insufficient heat input	Groove-defect	1) Material: ADC12
		2) N: 1500
		3) V: 750
		4) F: 6.9
Overheating/ Excessive heat input	Rough surface or Flash defect	1) Material: ADC12
		2) N: 1500
		3) V: 250
		4) F: 14.2

Authors	CRTT-FSW tool geometry	FSW process parameters	Remarkable effects of NRSA-FSW
Alloy, Tool Material	a) PiT/SeD	FSW process parameters	Remarkable effects of NRSA-FSW
Kumari et al. [¹²⁵125 Kumari K, Pal SK, Singh SB. S. BratSingh, Friction stir welding by using counter-rotating twin tool. Journal of Materials Processing Technology. 2015;215:132-141. http://dx.doi.org/10.1016/j.jmatprotec.2014.07.031. http://dx.doi.org/10.1016/j.jmatprotec.2... ]	SD(PiT/SeD): 16/16	N_P: 900-1800	1. Enhances the stirring effect of the tool and reduces the tunnel defect to minimum.
AA1100	PL(PiT/SeD):: 2/2	V: 16-63	2. Except flashes the defect-free joints are observed in higher welding and rotational speeds.
H: 2.5	PD: 5	Z: NA
TM: SS316 steel	PP: cylindrical pin/cylindrical pin	T: NA
		F: NA
Jain et al. [¹²⁶126 Jain R, Kumari K, Pal SK, Singh SB. Counter rotating twin-tool system in friction stir welding process: A simulation study. Journal of Materials Processing Technology. 2018;255:121-128. http://dx.doi.org/10.1016/j.jmatprotec.2017.11.043. http://dx.doi.org/10.1016/j.jmatprotec.2... ]	SD(PiT/SeD): 16/16	N_P: 900-1800	1. Enhances the flow of material from AS to RS in the SZ.
AA1100	PL(PiT/SeD): 2.6/2.6	V: 16-63	2. Significantly reduces the chances of defects in the former due to enhanced stirring effect of CRTT.
H: 3	PD: 5	Z: 0.1
TM: H13 steel	PP: cylindrical pin/cylindrical pin	T: 0°
		F: NA

Authors	RDR tool geometry	FSW process parameters	Remarkable effects of RDR-FSW
Alloy, Tool Material	RDR tool geometry	FSW process parameters	Remarkable effects of RDR-FSW
Li and Liu [¹³¹131 Li JQ, Liu HJ. Characteristics of the reverse dual-rotation friction stir welding conducted on 2219-T6 aluminum alloy. Materials & Design. 2013;45:148-154. http://dx.doi.org/10.1016/j.matdes.2012.08.068. http://dx.doi.org/10.1016/j.matdes.2012.... ]	Assisted SD: 14	N_S: 800	1. Improve tensile strength, and defect-free weld joints are produced due to the extreme stirring action of tool.
AA2219-T6	Mean PD: 4.52	N_P: 800	2. Grain structure becomes more refined and distributed uniformly in the weld nugget.
H: 5	PL: 4.8	V: 150
TM: NA	PP: Conical threaded pin	Z: 0.2
		T: 2.5º
		F: NA
Li and Liu [¹³⁵135 Li JQ, Liu HJ. Effects of the reversely rotating assisted shoulder on microstructures during the reverse dual-rotation friction stir welding. Journal of Materials Science and Technology. 2015;31(4):375-383. http://dx.doi.org/10.1016/j.jmst.2014.07.020. http://dx.doi.org/10.1016/j.jmst.2014.07... ]	Assisted SD: 14	N_S: 800	1. Higher grain refinement was observed at weld nugget, but the grains' size increases towards the heat-affected zone.
AA2219-T6	Mean PD: 4.52	N_P: 800	2. Precipitates are finer in TMAZ and HAZ compared to conventional FSW.
H: 5	PL: 4.8	V: 200	3. Decrease in the plastic flow of material because the flow is constrained below the reversely rotating tool.
TM: NA	PP: Conical threaded pin	Z: 0.2
		T: 2.5º
		F: NA
Li and Liu [¹³⁸138 Li JQ, Liu HJ. Optimization of welding parameters for the reverse dual-rotation friction stir welding of a high-strength aluminum alloy 2219-T6. International Journal of Advanced Manufacturing Technology. 2014;76(5-8):1469-1478. http://dx.doi.org/10.1007/s00170-014-6352-z. http://dx.doi.org/10.1007/s00170-014-635... ]	Assisted SD: 14	N_S: 200-800	1. Optimized process parameters of welding show better tensile strength than conventional FSW.
AA2219-T6	Mean PD: 4.52	N_P: 200-800	2. Reduction of total welding torque was found due to reverse rotation of shoulder and pin.
H: 5	PL: 4.8	V: 150-250
TM: NA	PP: Conical threaded pin	Z: 0.2
		T: 2.5º
		F: NA
Jamshidi Aval and Loureiro [¹³⁹139 Jamshidi Aval H, Loureiro A. Effect of reverse dual rotation process on properties of friction stir welding of AA7075 to AISI304. Transactions of Nonferrous Metals Society of China. 2019;29(5):964-975. http://dx.doi.org/10.1016/S1003-6326(19)65005-3. http://dx.doi.org/10.1016/S1003-6326(19)... ]	Assisted SD: 14	N_S: 600	1. The slower rotational speed of assisted shoulder reduces the amount of intermetallic compounds formed at the weld interface of lap joints.
AA7075-T6, AISI304 Stainless steel	PD: 5	N_P: 1000	2. Higher grain refinement is achieved in the nugget zone due to the slower rotational speed of assisted shoulder.
H: 2,1	PL: 2.1	V: 120
TM: NA	PP: Cylindrical pin	Z: 0.2
		T: 2.5º
		F: NA
Zhou et al. [¹⁴⁵145 Zhou L, Zhang RX, Hu XY, Guo N, Zhao HH, Huang YX. Effects of rotation speed of assisted shoulder on microstructure and mechanical properties of 6061-T6 aluminum alloy by dual-rotation friction stir welding. International Journal of Advanced Manufacturing Technology. 2019;100(1-4):199-208. http://dx.doi.org/10.1007/s00170-018-2570-0. http://dx.doi.org/10.1007/s00170-018-257... ]	Assisted SD: 14	N_S: 400-1200	1. By increasing shoulder rotational speed, defect-free joints and enlarged weld zone were attained.
AA6061-T6	PD: 3.45-6.2	N_P: 1200	2. Higher tensile strength and microhardness value was found compared to conventional FSW.
H: 5	(from pin tip to root)	V: 200
TM: NA	PL: 4.8	Z: 0.1
	PP: Conical threaded pin	T: 3º
		F: NA
Liu et al. [¹³²132 Liu HJ, Li JQ, Duan WJ. Research on reverse dual rotation friction stir welding process. Proceedings of the 1st International Joint Symposium on Joining and Weldin. 2013:25-32. http://dx.doi.org/10.1533/978-1-78242-164-1.25. http://dx.doi.org/10.1533/978-1-78242-16... ]	Assisted SD: 14	N_S: 1000
AA2219-T6	Mean PD: 4.52	N_P: 800	1. The reverse rotation of the tool shoulder and pin reduces the microstructural asymmetry of the weld nugget.
H: 5	PL: 4.8	V: 250	2. Increase in welding efficiency was found due to slower and higher rotational rate of shoulder and pin.
TM: NA	PP: Conical threaded pin	Z: 0.2
		T: 2.5º
		F: NA
Shi et al. [¹⁰⁶106 Shi L, Wu CS, Liu HJ. The effect of the welding parameters and tool size on the thermal process and tool torque in reverse dual-rotation friction stir welding. International Journal of Machine Tools & Manufacture. 2015;91:1-11. http://dx.doi.org/10.1016/j.ijmachtools.2015.01.004. http://dx.doi.org/10.1016/j.ijmachtools.... ]	Assisted SD: 14	N_S: 600-800
AA2024	PD: 4-6	N_P: 800-1200	1. In this numerical analysis non-axisymmetric heat generation rate was found at the shoulder-work piece contact, the peak value of heat generation rate was found maximum in front of the tool.
H: 5	(from pin tip to root)	V: 60-80	2. Decrease in the total net torque value was found due to the reverse rotation of the pin and shoulder.
TM: NA	PL: 4.8	Z: NA
	PP: Conical threaded pin	T: NA
		F: NA

Authors	SRFSW tool geometry	FSW process parameters	Remarkable effects of SRFSW
Alloy, Tool Material	SRFSW tool geometry	FSW process parameters	Remarkable effects of SRFSW
Liu et al. [¹⁶⁷167 Liu HJ, Hou JC, Guo H. Effect of welding speed on microstructure and mechanical properties of self-reacting friction stir welded 6061-T6 aluminum alloy. Materials & Design. 2013;50:872-878. http://dx.doi.org/10.1016/j.matdes.2013.03.105. http://dx.doi.org/10.1016/j.matdes.2013.... ]	USD: 18	N: 600	1. By increasing welding speed, defects such as band pattern reduce and improve weld joint tensile strength.
AA6061-T6	LSD: 16	V: 50-200	2. The tensile strength of defect-free weld joint with increase in welding speed reaches equivalent to 69% of base metal.
H: 4	PD: 8	Z: 0.1
TM: NA	PL: NA	T: NA
	PP: Cylindrical pin	F: NA
Sued et al. [¹⁶⁸168 Sued MK, Pons D, Lavroff J, Wong EH. Design features for bobbin friction stir welding tools: development of a conceptual model linking the underlying physics to the production process. Materials & Design. 2014;54:632-643. http://dx.doi.org/10.1016/j.matdes.2013.08.057. http://dx.doi.org/10.1016/j.matdes.2013.... ]	USD (scrolled): 8	N: 700	1. The effect of different pin profiles were studied and sound weld was found in case of 4 sided flat square pin.
AA6061-T6	LSD (scrolled): 8	V: 80	2. Essential compression effect during welding was produced by using this tool which increases hardness with decrease in tensile strength of weld joint towards clamp side.
H: 4	PD: NA	Z: 0.1
TM: NA	PL: NA	T: NA
	PP: Cylindrical threaded, threaded with 3flat, threaded with 4 flat, 4 sided flat square pin	F: NA

Wan et al. [¹⁷⁴174 Wan L, Huang Y, Lv Z, Lv S, Feng J. Effect of self-support friction stir welding on microstructure and microhardness of 6082-T6 aluminum alloy joint. Materials & Design. 2014;55:197-203. http://dx.doi.org/10.1016/j.matdes.2013.09.073. http://dx.doi.org/10.1016/j.matdes.2013.... ]	USD: 14	N: 800	1. Grain refinement takes place in upper and lower layer of weld joint, because of over aging effect and coarser second phase particles.
AA6082-T6	LSD: 9	V: 50-200	2. Hourglass-shaped weld were attained using this tool with no obvious change in grain structure and size compared to base metals in HAZ.
H: 5	PD: NA	Z: 0.1
TM: High speed steel	PL: 4.6	T: 4º
	PP: Conical threaded pin	F: NA
Esmaily et al. [¹⁶⁶166 Esmaily M, Mortazavi N, Osikowicz W, Hindsefelt H, Svensson JE, Halvarsson M, et al. Bobbin and conventional friction stir welding of thick extruded AA6005-T6 profiles. Materials & Design. 2016;108:114-125. http://dx.doi.org/10.1016/j.matdes.2016.06.089. http://dx.doi.org/10.1016/j.matdes.2016.... ]	USD: 24	N: 500-1200	1. Formations of kissing bonds take place at the lower weld surface of conventional FSW which are minimized by using bobbin tool.
AA6005-T6	LSD: 24	V: 500-1200	2. Heat generation is higher due to which grain refinement takes place from SZ to AS in bobbin tool assisted FSW.
H: 10	PD: 8-10	Z: 0.1
TM: NA	(from pin tip to root)	T: 2º
	PL: 9.8	F: NA
	PP: Tri flat conical threaded pin
Wan et al. [¹⁷²172 Wan L, Huang Y, Guo W, Lv S, Feng J. Mechanical Properties and Microstructure of 6082-T6 Aluminum Alloy Joints by Self-support Friction Stir Welding. Journal of Materials Science and Technology. 2014;30(12):1243-1250. http://dx.doi.org/10.1016/j.jmst.2014.04.009. http://dx.doi.org/10.1016/j.jmst.2014.04... ]	USD: 14	N: 800	1. Welding speed is a key parameter for enhancing the weld joint quality because at lower welding speeds the band pattern and series of onion rings are formed which can be eliminated by optimizing the welding speed.
AA6082-T6	LSD: 9	V: 10-200	2. Increase in welding speed reduces the tunnel defect as well as enhances the tensile strength of weld joint.
H: 5	PD: NA	Z: 0.1
TM: NA	PL: 4.6	T: 4º
	PP: Conical threaded pin	F: NA
Hou et al. [¹⁷⁰170 Hou JC, Liu HJ, Zhao YQ. Influences of rotation speed on microstructures and mechanical properties of 6061-T6 aluminum alloy joints fabricated by self-reacting friction stir welding tool. International Journal of Advanced Manufacturing Technology. 2014;73(5-8):1073-1079. http://dx.doi.org/10.1007/s00170-014-5857-9. http://dx.doi.org/10.1007/s00170-014-585... ]	USD: 18	N: 400-800	1. Increasing the difference in upper and lower shoulder size bring about defects.
AA6061-T6	LSD: 16, 14, 12	V: 150	2. Voids are formed towards AS of the weld joint. Such defects were eliminated by reducing the rotational speed of tool.
H: 4	PD: 8	Z: 0.06
TM: NA	PL: NA	T: NA
	PP: Cylindrical pin	F: NA
Okamoto et al. [¹⁷¹171 Okamoto K, Sato A, Park SH, Hirano S. Microstructure and Mechanical Properties of FSWed Aluminum Extrusion with Bobbin Tools. Materials Science Forum. 2012;709:990-995. http://dx.doi.org/10.4028/www.scientific.net/MSF.706-709.990. http://dx.doi.org/10.4028/www.scientific... ]	USD: 20	N: 600-1000	1. By decreasing the pinching gap between shoulders enhances the weld joint quality.
AA6082-T6, 6068-T6, 6061-T6, A6N01-T5	LSD: 20	V: 30-1000	2. The oxide remnant so called “lazy S” was eliminated by using convex scroll shoulder shaped bobbin tool.
H: 5.95	PD: 10	Z: 0.1
TM: Tool steel	PL: NA	T: NA
	PP: Threaded pin with 3 flats having convex scroll shoulder	F: NA
Zhang et al. [¹⁶⁵165 Zhang H, Wang M, Zhang X, Yang G. Microstructural characteristics and mechanical properties of bobbin tool friction stir welded 2A14-T6 aluminum alloy. Materials & Design. 2015;65:559-566. http://dx.doi.org/10.1016/j.matdes.2014.09.068.]	USD: 16	N: 400	1. The scrolled shaped shoulder enhances the material flow and eliminates the requirement of tool tilting.
2A14-T6	LSD: 16	V: 25-150	2. The FSW parameters must be optimized first in order to reduce the formation of ellipse and triangular shaped region.
H: 6	PD: 8	Z: 0.07
TM: NA	PL: NA	T: NA
	PP: Tri flat cylindrical pin (scrolled shoulder)	F: NA
Zhou et al. [¹⁵³153 Zhou L, Li GH, Liu CL, Wang J, Huang YX, Feng JC, et al. Microstructural characteristics and mechanical properties of Al–Mg–Si alloy self-reacting friction stir welded joints. Science and Technology of Welding and Joining. 2017;22(5):438-445. http://dx.doi.org/10.1080/13621718.2016.1251733. http://dx.doi.org/10.1080/13621718.2016.... ]	USD: 18	N: 400	1. Defects like flashes and pores are formed at higher and lower welding speeds.
AA6061-T6	LSD: 16	V: 150-450	2. Tensile properties of weld joint increases as well as refined grains are achieved at higher welding speed.
H: 5	PD: 8	Z: 0.1
TM: NA	PL: NA	T: NA
	PP: Tetra flat cylindrical pin	F: NA
Zhao et al. [¹⁷⁵175 Zhao Y, Wang C, Dong C. Microstructural characteristics and mechanical properties of water cooling bobbin-tool friction stir welded 6063-T6 aluminum alloy. MATEC Web of Conferences. 2018;03002. https://doi.org/10.1051/matecconf/201820603002. https://doi.org/10.1051/matecconf/201820... ]	USD: 16	N: 1200	1. In situ water mist was sprayed to the leading edge of top shoulder which reduces the peak temperature as well as enhances the weld joint properties.
AA6063-T6	LSD: 16	V: 200	2. Defect free joint and 11.4% increase in tensile strength was found in water cooling specimen as compared to as welded specimens.
H: 4	PD: 8	Z: 0.05
TM: NA	PL: 4	T: NA
	PP: Threaded cylindrical pin (spiral groove shoulder)	F: NA
Yang et al. [¹⁷⁶176 Yang C, Ni DR, Xue P, Xiao BL, Wang W, Wang KS, et al. Materials characterization a comparative research on bobbin tool and conventional friction stir welding of Al-Mg-Si alloy plates. Materials Characterization. 2018;145:20-28. http://dx.doi.org/10.1016/j.matchar.2018.08.027. http://dx.doi.org/10.1016/j.matchar.2018... ]	USD: 22	N: 300, 400, 600	1. Compared to normal FSW, in bobbin tool FSW the weld joint quality is independent of tool rotational speed.
AA6061-T4	LSD: 22	V: 50, 100, 150, 300	2. Weld nugget grains become more refined with increase in welding speed in both the conditions.
H: 6.35	PD: 8	Z: NA
TM: NA	PL: 6	T: NA
	PP: Threaded cylindrical pin (scrolled groove shoulder)	F: NA
Wang et al. [¹⁷³173 Wang FF, Li WY, Shen J, Wen Q. Improving weld formability by a novel dual-rotation bobbin toolfriction stir welding. Journal of Materials Science and Technology. 2017;1–5. http://dx.doi.org/10.1016/j.jmst.2017.11.001. http://dx.doi.org/10.1016/j.jmst.2017.11... ]	USD: 11	N: 400-1200	1. Bobbin FSW shows higher stability throughout the process as well as defect free joints can also be produced in a wider range of welding parameters.
AA2198-T851	LSD: 11	V: 42	2. The unbalanced forces at upper and lower surface enhance the material flow and eliminate weld defects such as voids.
H: 3.2	PD: 4	Z: 0.1
TM: NA	PL: NA	T: NA
	PP: Cylindrical pin	F: NA
Li et al. [¹⁷⁷177 Li GH, Zhou L, Luo SF, Du ZY, Feng JC, Meng FX. Microstructure and mechanical properties of self-reacting friction stir welded AA2219-T87 aluminium alloy. Science and Technology of Welding and Joining. 2020;25(2):142-149. http://dx.doi.org/10.1080/13621718.2019.1648719. http://dx.doi.org/10.1080/13621718.2019.... ]	USD: 24	N: 350	1. Increase in welding speeds avoids the tunnel defect. However, at extreme welding speed the weld joint remnants provide an easier path for crack initiation leads to reduction of weld strength.
AA2219-T87	LSD: 24	V: 250-450	2. Improper heat dissipation through bottom shoulder increases the lower surface average grain size of weld nugget
H: 8	PD: 12	Z: 0.1
TM: NA	PL: NA	T: NA
	PP: Cylindrical pin	F: NA
	(Cavity feature in shoulders)
Goebel et al. [¹⁷⁸178 Goebel J, Reimann M, Norman A, dos Santos JF. Semi-stationary shoulder bobbin tool friction stir welding of AA2198-T851. Journal of Materials Processing Technology. 2017;245:37-45. http://dx.doi.org/10.1016/j.jmatprotec.2017.02.011. http://dx.doi.org/10.1016/j.jmatprotec.2... ]	USD: 15	N: 400, 600	1. A tool with one stationary and other rotating shoulder was used and defect less weld with high surface finish were attained on the stationary side of tool.
AA2198-T851	LSD: 15	V: 200, 500	2. High quality weld joints are achieved having hardness and ultimate tensile strength efficiency of 77%^ and 82%.
H: 3	PD: 7	Z: NA
TM: Pin-MP159, shoulder- X38CrMoV5-1	PL: NA	T: NA
	PP: Cylindrical pin	F: 2.5, 4, 5
	(Scrolled shoulder)

Authors	In-Situ rolling tool/FSW tool geometry	FSW process parameters	Remarkable effects of IRFSW
Alloy, Tool Material	In-Situ rolling tool/FSW tool geometry	FSW process parameters	Remarkable effects of IRFSW
Huang et al. [¹⁸⁷187 Huang Y, Wan L, Lv S, Liu H, Feng J. Gradient micro-structured surface layer on aluminum alloy fabricated by in situ rolling friction stir welding. Materials & Design. 2013;52:821-827. http://dx.doi.org/10.1016/j.matdes.2013.06.026. http://dx.doi.org/10.1016/j.matdes.2013.... ]	Roller Type: Ball	N: 600	1. Low temperature rolling of upper surface improves the hardness value of upper surface as well as tensile strength of weld joint.
AA2219	D_B: 8, R_D: 0.05	V: 300
H: 3mm	SD: 14mm	Z: 0.1
TM: Tool steel	PD: 2.6mm	T: NA
	PL: NA	F: NA
	PP: Threaded conical pin
Huang et al. [¹⁰⁵105 Huang Y, Wan L, Lv S, Zhang J, Fu G. In situ rolling friction stir welding for joining AA2219. Materials & Design. 2013;50:810-816. http://dx.doi.org/10.1016/j.matdes.2013.03.088. http://dx.doi.org/10.1016/j.matdes.2013.... ]	Roller Type: Ball	N: 600	1. Incorporation of rolling tool eliminates flash defects and enhances mechanical properties of weld joint.
AA2219	D_B: 8, R_D: 0.05	V: 100-500	2. Percentage increase in Tensile strength and hardness value is 13% and 20%
H: 3mm	SD: 14mm	Z: 0.1
TM: Tool steel	PD: 2.6mm	T: NA
	PL: NA	F: NA
	PP: Threaded conical pin
Hassanifard et al. [¹⁹²192 Hassanifard S, Reyhani HA, Nabavi-Kivi A, Varvani-Farahani A. An experimental study of rolled friction-stir-welded aluminum 6061-T6 joints subjected to static and fatigue loading conditions. Journal of Materials Engineering and Performance. 2020;29(7):4493-4505. http://dx.doi.org/10.1007/s11665-020-04949-w. http://dx.doi.org/10.1007/s11665-020-049... ]	Roller Type: Ball	N: 1400	1. In situ rolling of smaller and larger rolling balls enhances the weld strength of joint by 25 and 40% as compared to conventional FSW process.
AA6061-T6	D_B: 6,8, R_D: 0.05-0.7	V: 36	2. grains becomes more refined and uniform especially in heat affected zone as well as improves the fatigue life of the weld joint compared with those of as welded samples.
H: 5mm	SD: 18mm	Z: 1
TM: NA	PD: 6mm	T: NA
	PL: 2.6	F: NA
	PP: Conical pin
Du et al. [¹⁹⁰190 Du C, Pan Q, Chen S, Tian S. Effect of rolling on the microstructure and mechanical properties of 6061-T6 DS-FSW plate. Materials Science and Engineering A. 2020;772:138692. http://dx.doi.org/10.1016/j.msea.2019.138692. http://dx.doi.org/10.1016/j.msea.2019.13... ]	Roller Type: Cylindrical	N: 1200	1. The double sided friction stir welded sample of 6mm thickness was rolled to 4, 3, and 2 mm thickness due to which it improves dislocation density in stirred zone.
AA6061-T6	D_R: NA, W_R: NA	V: 500	2. All the strengthening effect such as solid solution strengthening, precipitating strengthening and grain refine strengthening were stronger than base metals.
H: 6	R_D: 2,3,4, F_R: NA	Z: NA
TM: NA	SD: NA	T: NA
	PD: NA	F: NA
	PL: 4.3
	PP: Threaded conical pin
Altenkirch et al. [¹⁹³193 Altenkirch J, Steuwer A, Withers PJ, Williams SW, Poad M, Wen SW. Residual stress engineering in friction stir welds by roller tensioning. Science and Technology of Welding and Joining. 2009;14(2):185-192. http://dx.doi.org/10.1179/136217108X388624. http://dx.doi.org/10.1179/136217108X3886... ]	Roller Type: Cylindrical	N: 800	1. Author suggests that the post weld roller tensioning is the cheapest method of reducing the residual stress with lesser force requirement. Moreover, a load of 20 KN is sufficient for reversing the sign of residual stress.
AA2024-T3, AA2199-T8	D_R: 100, W_R: 29	V: 200-400
H: 5	R_D: NA, F_R: 10,20,30,40	Z: NA
TM: MP156	SD: 13	T: NA
	PD: 5	F: 1.3
	PL: 4.35
	PP: Threaded pin
Huang et al. [¹⁹¹191 Huang YX, Wan L, Lv SX, Zhang Z, Liu HJ. New technique of in situ rolling friction stir welding. Science and Technology of Welding and Joining. 2012;17(8):636-642. http://dx.doi.org/10.1179/1362171812Y.0000000056. http://dx.doi.org/10.1179/1362171812Y.00... ]	Roller Type: Ball	N: 800	1. The rolling tool pressure smoothen the weld surface asperities as well as reduces excessive flash formation.
AA2219	D_B: 8, R_D: 0.05	V: 200	2. As compared to conventional FSW, this new technique reduces the residual stress and enhances the resistance to corrosion.
H: 3	SD: 14	Z: NA
TM: Tool steel	PD: NA	T: 2.5º
	PL: 2.6	F: NA
	PP: Conical threaded pin
Ghisvand et al. [¹⁹⁴194 Ghiasvand A, Kazemi M, Jalilian MM, Kheradmandan H. Investigation of exerted force on roller and roller width effects on residual stresses in direct and indirect rolling of FSW of SU304 steel. Journal of Stress Analysis. 2020;4(2):115-125. http://dx.doi.org/10.22084/jrstan.2020.20922.1127. http://dx.doi.org/10.22084/jrstan.2020.2... ]	Roller Type: Cylindrical	N: 500	1. Author investigated the role of direct and indirect rolling of FSW joints and found that at optimized width of roller (equal to tool diameter 20mm) the maximum tensile residual stress reduces by 57.3% for indirect rolling and 97.4% for direct rolling.
304 stainless steel,	D_R: 30, W_R: 10-30	V: 101.6
H: 3.18	R_D: NA, F_R: 2.5-12.5	Z: NA
TM: NA	SD: 19.05	T: NA
	PD: 6.35	F: 31.138
	PL: 3
	PP: NA
Wen et al. [¹⁹⁵195 Wen SW, Colegrove PA, Williams SW, Morgan SA, Wescott A, Poad M. Rolling to control residual stress and distortion in friction stir welds. Science and Technology of Welding and Joining. 2010;15(6):440-447. http://dx.doi.org/10.1179/136217110X12785889549787. http://dx.doi.org/10.1179/136217110X1278... ]	Roller Type: Cylindrical	N: NA	1. Finite element analysis was carried out to understand the reduction in residual stress induced by FSW, for three rolling methods i.e. in situ roller tensioning (ISRT), in situ direct rolling (ISDR), post weld direct rolling (PWDR). Of the three methods the PWDR showed a significant reduction of longitudinal residual stress as well as distortion of weld joints at similar roller forces.
AA2024-T3	D_R: 100, W_R: 20	V: 300
H: 3.2	R_D: NA, F_R: 10-68	Z: NA
TM: NA	SD: 18	T: NA
	PD: 2-4	F: NA
	(from pin tip to root)
	PL: 3.2
	PP: Conical pin

FSW assisted tool systems	Effect of FSW process parameters and pin profile on weld quality
Non rotational shoulder assisted FSW (NRSA-FSW)	The static shoulder designed in NRSA-FSW is used for minimizing overheating defect such as flashes. Conical/tapered threaded pin profile produces defect-less joint with smooth weld surface. Since the shoulder is stationary higher tool pin rotational speed was preferable to generate sufficient heat input for producing the defect-less joints.
Counter rotating twin tool FSW (CRTT-FSW)	Since this variant (CRTT-FSW) is in initial stage and only few literatures were reported so far. Additionally, this FSW variant is found very crucial to enhance the stirring effect of tool due to use of twin tool rotates in opposite direction. In case of CRTT higher frictional heat is generated therefore, low translational and rotational speed is preferable.
Reverse dual rotation FSW (RDR-FSW)	Overheating of weld joint at high speeds leads to the formation of flash defects and undesirable reduction in weld thickness. The reverse dual rotation of pin and shoulder reduces the overheating and enhances material flow. Authors performed welding in a wide range of tool shoulder and pin speeds. In this case improved mechanical properties were observed at a tool rotational speed of N_S: 800rpm, N_P: 800rpm and welding speed of 150-250mm/min. In most of the cases the conical threaded pin profile displays fine grains and improves material flow.
Self-reacting/self-support/ Bobbin tool FSW	Self-reacting or bobbin tool is designed to eliminate the requirement of plunge force and root flaws of conventional friction stir weld joints.
Self-reacting/self-support/ Bobbin tool FSW	Threaded cylindrical pin and scrolled type shoulder improves the flow of material in both the upper and lower parts of the weld joint. In this case higher welding speed and medium tool rotational speed is preferable to attain high quality weld joints.
In situ rolling FSW (IRFSW)	In situ rolling of friction stir weld joints reduces the residual stress and eliminate flash defect. Usually conical threaded pin profile generates sufficient heat input and enhances downward movement of plasticized material. Medium tool rotational speed and welding speed were desirable to enhance properties of the weld joint.

[1] E-mails: surendralader@gmail.com (SKL), mayuri.prod@nitjsr.ac.in (MB), rballav.prod@nitjsr.ac.in (RB), swarupbag@iitg.ac.in (SB)

Brasil

Brasil

Recent Developments in Friction Stir Welding Tools for Weld Bead Defects Minimization – A Review

Abstract