Microstructural evolution in friction self-piercing riveted aluminum alloy AA7075-T6 joints

doi:10.1016/j.jmst.2020.12.023

Abstract

Abstract:

Friction self-piercing riveting (F-SPR) is an emerging technique for low ductility materials joining, which creates a mechanical and solid-state hybrid joint with a semi-hollow rivet. The severe plastic deformation of work materials and localized elevated temperatures during the F-SPR process yield complex and heterogeneous microstructures. The cut-off action of the work materials by the rivet further complicates the material flow during joint formation. This study employed the F-SPR process to join AA7075-T6 aluminum alloy sheets and systematically investigated the microstructural evolutions using electron backscatter diffraction (EBSD) techniques. The results suggested that as the base material approached the rivet, grains were deformed and recrystallized, forming two distinct fine grain zones (FGZs) surrounding the rivet and in the rivet cavity, respectively. Solid-state bonding of aluminum sheets occurred in the FGZs. The formation of FGZ outside the rivet is due to dynamic recrystallization (DRX) triggered by the sliding-to-sticking transition at the rivet/sheet interface. The FGZ in the rivet cavity was caused by the rotation of the trapped aluminum, which created a sticking affected zone at the trapped aluminum/lower sheet interface and led to DRX. Strain rate gradient in the trapped aluminum drove the further expansion of the sticking affected zone and resulted in grain refinement in a larger span.

Key words: Friction self-piercing riveting, Semi-hollow rivet, Aluminum alloy, Affected zone, Dynamic recrystallization

Yunwu Ma, Sizhe Niu, Huihong Liu, Yongbing Li, Ninshu Ma. Microstructural evolution in friction self-piercing riveted aluminum alloy AA7075-T6 joints[J]. J. Mater. Sci. Technol., 2021, 82: 80-95.

Figures/Tables 26

Fig. 1. Schematic of friction self-piercing riveting process. (a) Positioning, (b) friction softening, (c) quick stop, (d) tooling release.

Table 1 Joint efficiencies of typical FSW joints of aluminum alloys.

Aluminum type	Base material	Ultimate tensile strength of base material (UTS_BM)	Joint efficiency ($\frac{UT{{S}_{\text{FSWjoint}}}}{UT{{S}_{\text{BM}}}}\times %$)	Reference
Heat-treatable	AA2024-T6	477 MPa	76 %	[24]
	AA2219-T87	491 MPa	69 %	[25]
	AA6005A-T6	294 MPa	79 %	[26]
	AA6061-T6	279 MPa	65 %	[27]
	AA7075-T6	564 MPa	80 %	[28]
	AA7085-T7452	500MPa	82 %	[29]
Non-heat treatable	AA5083-O	302 MPa	100 %	[24]
Non-heat treatable	AA5456-H112	324 MPa	97 %	[30]

Table 2 Mechanical properties of 35CrMo steel and AA7075-T6 aluminum alloy.

Material	Elastic modulus (GPa)	Yield strength (MPa)	Ultimate tensile strength (MPa)	Elongation (%)
35CrMo	211	835	985	≥12
AA7075-T6	72	479	586	13.6

Table 3 Chemical composition of 35CrMo steel and aluminum alloy AA7075-T6 (wt.%).

35CrMo	Mn	Si	Cr	Mo	C	S	P	Fe
35CrMo	0.75	0.3	1.05	0.2	0.34	≤0.03	≤0.03	Bal.
AA7075-T6	Mg	Zn	Cu	Mn	Si	Ti	Cr	S	Fe	Al
AA7075-T6	2.42	5.72	1.43	0.03	0.12	0.03	0.19	0.12	0.23	Bal.

Fig. 2. 3D morphologies and key dimensions of the rivet and the pip die. (a) Rivet, (b) pip die. Unit: mm.

Fig. 3. Macro profiles of the F-SPR joint made with 3600 rpm rotational speed and 2.0 mm/s feed rate. (a) The etched cross-section in ND-RD plane, (b) b-b section in TD-RD plane, (c) c-c section in TD-RD plane, (d)-(g) zoom-in views at the rivet-sheet interfaces.

Fig. 4. Macro profiles of the F-SPR joint made with 3600 rpm rotational speed and 8.0 mm/s feed rate. (a) The etched cross-section in ND-RD plane, (b) b-b section in TD-RD plane, (c) c-c section in TD-RD plane, (d)-(g) zoom-in views at the rivet-sheet interfaces.

Fig. 5. Microstructures of the as-received AA7075-T6 in three different orthogonal directions. ND: normal direction; TD: transverse direction; RD: rolling direction.

Fig. 6. EBSD results of the as-received AA7075-T6 in the ND-RD plane. (a) Inverse pole figure, (b) grain boundary map, (c) fractions of misorientation angles.

Fig. 7. Optical microscope images of aluminum outside of the rivet in the 3600 rpm-2.0 mm/s F-SPR joint. (a) The middle of the upper sheet, (b) the middle of the lower sheet, (c) the lower sheet at the joint bottom.

Fig. 8. EBSD results of region 1 outside the rivet in Fig. 7(b). (a) Inverse pole figure, (b) grain boundary map, (c)-(e) fractions of misorientation angles in sub-zones I, II, and III, respectively. Arrows in (a) highlight the fine grain clusters.

Fig. 9. EBSD results of the region marked with a yellow box in Fig. 8(b). (a) Inverse pole figure, (b) grain boundary map, (c) fractions of misorientation angles.

Fig. 10. EBSD results of region 2 at the bottom of the joint in Fig. 7(c). (a) Inverse pole figure, (b) grain boundary map, (c) fractions of misorientation angles.

Fig. 11. Optical microscope images at the sheet-sheet interface outside the rivet in the 3600 rpm-2.0 mm/s F-SPR joint. (a) Left interface, (b) right interface.

Fig. 12. EBSD results of region 3 at the sheet-sheet interface in Fig. 11(b). (a) Inverse pole figure, (b) grain boundary map, (c) fractions of misorientation angles.

Fig. 13. Optical microscope images of aluminum in the rivet cavity in the 3600 rpm-2.0 mm/s F-SPR joint. (a) Upper portion showing coarse grains, (b) the boundary between coarse and fine grains, (c) lower position showing fine grains.

Fig. 14. EBSD results of region 4 in the rivet cavity in Fig. 13(a). (a) Inverse pole figure, (b) grain boundary map, (c) fractions of misorientation angles.

Fig. 15. EBSD results of region 5 in the rivet cavity in Fig. 13(c). (a) Inverse pole figure, (b) grain boundary map, (c) fractions of misorientation angles.

Fig. 16. Vickers hardness distribution maps of F-SPR joints under different process parameters. (a) 3600 rpm-2.0 mm/s, (b) 1800 rpm-2.0 mm/s, (c) 3600 rpm-8.0 mm/s.

Fig. 17. TEM bright field images of the aluminum microstructure in the 3600 rpm-2.0 mm/s joint. (a) AA7075-T6 base material, (b)-(d) zones I, II and III outside the rivet showing coarsened precipitates, (e) the upper portion inside rivet showing coarsened precipitates and partial dissolution, and (f) the lower portion inside rivet showing complete dissolution of precipitates.

Fig. 18. The measured reactive force and torque during the F-SPR process as functions of process time and the calculated heat input for different process parameter combinations. (a) Reactive force, (b) reactive torque, (c) heat input.

Fig. 19. Partition schematic of the affected zones in a typical F-SPR joint.

Fig. 20. Etched macro profiles of aluminum alloys surrounding the rivet at different feed depths of the 3600 rpm-2.0 mm/s F-SPR process. (a) 1.0 mm, (b) 2.0 mm, (c) 2.5 mm, (d) 3.0 mm, (e) 4.0 mm and (f) 5.3 mm.

Fig. 21. Microstructures at different rivet feed depths. (a)-(i) Locations A-I in Fig. 20.

Fig. 22. Friction conditions between rivet and aluminum alloy sheet in F-SPR. (a) Sliding, (b) sticking.

Fig. 23. Formation mechanism of the fine grain zone in the rivet cavity. The upper joint cross-sections correspond to Fig. 20(a)-(d) and (f), and the lower schematics illustrate the contact conditions between the trapped aluminum and the lower sheet.

References 55

[1]	K. Mori, Y. Abe, T. Kato, J. Mater. Process. Technol. 212 (9)(2012) 1900-1905. DOI URL
[2]	X. Zhang, X. He, F. Gu, A. Ball, J. Mater. Process. Technol. 268 (2019) 192-200. DOI URL
[3]	H. Jiang, S. Gao, G. Li, J. Cui, Mater. Des. 183 (2019), 108141. DOI URL
[4]	M. Jäckel, T. Grimm, D. Landgrebe, AIP Conf. Proc. 1769 (2016), 100010.
[5]	H. Duan, G. Han, M. Wang, X. Zhang, Z. Liu, Z. Liu, Mater. Des. 54 (2014) 14-424. DOI URL
[6]	X. Zhao, D. Meng, J. Zhang, Q. Han, Int. J. Adv. Manuf. Technol. 109 (9-12)(2020) 2409-2419. DOI URL
[7]	J.W. Wang, Z.X. Liu, Y. Shang, A.L. Liu, M.X. Wang, R.N. Sun, P.-C. Wang,ASME J. Manuf. Sci. Eng. 133 (3)(2011), 031009.
[8]	Y. Durandet, R. Deam, A. Beer, W. Song, S. Blacket, Mater. Des. 31 (SUPPL. 1)(2010) S13-S16. DOI URL
[9]	Y. Li, Z. Wei, Z. Wang, Y. Li, ASME J. Manuf. Sci. Eng. 135 (6)(2013), 061007. DOI URL
[10]	X. Liu, Y.C. Lim, Y. Li, W. Tang, Y. Ma, Z. Feng, J. Ni, J. Mater. Process. Technol. 237 (2016) 19-30. DOI URL
[11]	Y.C. Lim, C.D. Warren, J. Chen, Z. Feng, Joining of Lightweight Dissimilar Materials by Friction Self-Piercing Riveting, 2019, pp. 189-195.
[12]	Y. Ma, B. Yang, M. Lou, Y. Li, N. Ma, J. Mater. Process. Technol. 278 (2020), 116543. DOI URL
[13]	Y. Ma, H. Shan, S. Niu, Y. Li, Z. Lin, N. Ma, Engineering(2020).
[14]	Y. Ma, S. Niu, H. Shan, Y. Li, N. Ma, Automot. Innov. 3 (3)(2020) 242-249. DOI URL
[15]	Z. Shen, Y. Chen, J. Hou, X. Yang, A. Gerlich, Sci. Technol. Weld. Join. 20 (1)(2015) 48-57. DOI URL
[16]	M. Reimann, J. Goebel, J.F. dos Santos, Mater.Des. 132 (2017) 283-294.
[17]	W. Tao, Z. Yong, L. Xuemei, K. Matsuda, Mater. Sci. Eng. A 671 (2016) 7-16. DOI URL
[18]	B. Wang, B.-b. Lei, J.-x. Zhu, Q. Feng, L. Wang, D. Wu, Mater. Des. 87 (2015) 593-599. DOI URL
[19]	X. Zeng, P. Xue, L. Wu, D. Ni, B. Xiao, K. Wang, Z. Ma, J. Mater. Sci. Technol. 35 (6)(2019) 972-981. DOI
[20]	Y. Hu, H. Liu, S. Li, S. Du, D.P. Sekulic, Mater. Sci. Eng. A 731 (2018) 107-118. DOI URL
[21]	J. Min, J. Li, Y. Li, B.E. Carlson, J. Lin, ASME J. Manuf. Sci. Eng. 138 (5)(2015), 054501. DOI URL
[22]	M.D. Tier, T.S. Rosendo, J.F. dos Santos, N. Huber, J.A. Mazzaferro, C.P. Mazzaferro, T.R. Strohaecker, J. Mater. Process. Technol. 213 (6)(2013) 997-1005. DOI URL
[23]	A. Baqerzadeh Chehreh, M. Gratzel, J.P. Bergmann, F. Walther, Materials (Basel) 13 (14)(2020).
[24]	K. Nakata, Y.G. Kim, M. Ushio, T. Hashimoto, S. Jyogan, ISIJ Int. 40 (Suppl)(2000) S15-S19. DOI URL
[25]	A.P. Reynolds, W.D. Lockwood, T.U. Seidel, Mater. Sci.Forum 331-337 (2000) 1719-1724.
[26]	X. Liu, H. Liu, T. Wang, X. Wang, S. Yang, J. Mater. Sci. Technol. 34 (1)(2018) 102-111. DOI URL
[27]	A.H. Baghdadi, A. Rajabi, N.F.M. Selamat, Z. Sajuri, M.Z. Omar, Mater. Sci. Eng. A 754 (2019) 728-734. DOI URL
[28]	G. İpekoğlu, S. Erim, G. Çam, Int. J. Adv. Manuf. Technol. 70 (1)(2014) 201-213. DOI URL
[29]	W. Xu, Y. Luo, W. Zhang, M. Fu, J. Mater. Sci. Technol. 34 (1)(2018) 173-184. DOI URL
[30]	M. Mardalizadeh, M. Khandaei, M.A. Safarkhanian, J. Adhes. Sci. Technol.(2020) 1-20.
[31]	Y.W. Ma, Y.B. Li, Z.Q. Lin, ASME J. Manuf. Sci. Eng. 141 (4)(2019), 041005-041005-11. DOI URL
[32]	Y. Li, Y. Ma, M. Lou, Z. Lin, Google Patents, 2019.
[33]	F. Liu, T. Nelson, Mater. Des. 115 (2017) 467-478. DOI URL
[34]	H. Miura, T. Sakai, H. Hamaji, J.J. Jonas, Scr. Mater. 50 (1)(2004) 65-69. DOI URL
[35]	J. Zhang, X.S. Feng, J.S. Gao, H. Huang, Z.Q. Ma, L.J. Guo, J. Mater. Sci. Technol. 34 (1)(2018) 219-227. DOI
[36]	H. Liu, H. Fujii, Mater. Sci. Eng. A 711 (2018) 140-148. DOI URL
[37]	R.S. Mishra, Z.Y. Ma, Mater. Sci. Eng. R 50 (1)(2005) 1-78. DOI URL
[38]	H. Ji, Y. Deng, H. Xu, S. Lin, W. Wang, H. Dong, Mater. Des. 192 (2020), 108729. DOI URL
[39]	Z. Zhang, C. He, Y. Li, L. Yu, S. Zhao, X. Zhao, J. Mater. Sci. Technol. 43 (2020) 1-13. DOI URL
[40]	A. Gerlich, M. Yamamoto, T.H. North, Metall. Mater. Trans. A 38 (6)(2007) 1291-1302. DOI URL
[41]	D. Richard, P.N. Adler, Metall. Trans. A 8 (7)(1977) 1177-1183. DOI URL
[42]	J.Q. Su, T.W. Nelson, R. Mishra, M. Mahoney, Acta Mater. 51 (3)(2003) 713-729. DOI URL
[43]	A.H. Feng, D.L. Chen, Z.Y. Ma, Metall. Mater. Trans. A 41a (4)(2010) 957-971.
[44]	J. Zhang, P. Upadhyay, Y. Hovanski, D.P. Field, Metall. Mater. Trans. A 49 (1)(2017) 210-222. DOI URL
[45]	M. Ahmed, S. Ataya, M.E.-S. Seleman, H. Ammar, E. Ahmed, J. Mater. Process. Technol. 242 (2017) 77-91. DOI URL
[46]	A. Gerlich, G. Avramovic-Cingara, T.H. North, Metall. Mater. Trans. A 37 (9)(2006) 2773-2786. DOI URL
[47]	T.R. McNelley, S. Swaminathan, J.Q. Su, Scr. Mater. 58 (5)(2008) 349-354. DOI URL
[48]	Y. Hu, H. Liu, H. Fujii, K. Ushioda, J. Manuf. Processes 56 (2020) 362-371. DOI URL
[49]	R. Prasad Mahto, S.K. Pal, J. Manuf. Processes 55 (2020) 103-118. DOI URL
[50]	C. Yang, C. Wu, L. Shi, Sci. Technol. Weld. Join. 25 (4)(2019) 345-358. DOI URL
[51]	H. Schmidt, J. Hattel, J. Wert, Modell. Simul. Mater. Sci. Eng. 12 (1)(2004) 143-157. DOI URL
[52]	H. Su, C.S. Wu, A. Pittner, M. Rethmeier, Energy 77 (2014) 720-731. DOI URL
[53]	G. Chen, G. Wang, Q. Shi, Y. Zhao, Y. Hao, S. Zhang, J. Manuf. Processes 41 (2019) 1-9. DOI URL
[54]	G.Q. Chen, H. Li, G.Q. Wang, Z.Q. Guo, S. Zhang, Q.L. Dai, X.B. Wang, G. Zhang, Q.Y. Shi, Int. J. Mach. Tools Manuf. 124 (2018) 12-21. DOI URL
[55]	J. Min, Y. Li, J. Li, B.E. Carlson, J. Lin, J. Mater. Process. Technol. 222 (2015) 268-279. DOI URL