Achieving superior mechanical properties in friction lap joints of copper to carbon-fiber-reinforced plastic by tool offsetting

doi:10.1016/j.jmst.2018.04.015

Abstract

Abstract:

It is a challenge to achieve a sound welded metal/carbon-fiber-reinforced thermoplastic (CFRTP) joint with high strength and few bubbles. In this study, sound lap joints of Cu and CFRTP were obtained by friction lap joining (FLJ) directly at rotation rates of 600-2000 rpm, with the welding tool at the joint center and offsetting the tool 7 mm away from the center toward the retreating side, respectively. Tool offsetting reduced the non-uniform temperature distribution in the lap joints resulting from the high conductivity of Cu, which not only enhanced the tensile shear force from 0.89-2.25 kN to 1.71-3.54 kN, with the maximum increasing rate of 135%, but also reduced the bubble area to only 19% of the original level of 2000 rpm. It is the first time to report a high-quality Cu/CFRTP joint with a high strength and few bubbles. The large increase of the strength after tool offsetting was attributed to the increase of the joining area, the decrease of bubbles and the decrease of the CFRTP degradation. The details on the generation, quantitative distribution and expulsion of the bubbles in the FLJ joints were discussed.

Key words: Hybrid joining, Plastic, Metal, Carbon-fiber-reinforced plastic, Properties

L.H. Wu, K. Nagatsuka, K. Nakata. Achieving superior mechanical properties in friction lap joints of copper to carbon-fiber-reinforced plastic by tool offsetting[J]. J. Mater. Sci. Technol., 2018, 34(9): 1628-1637.

Figures/Tables 14

Fig 1. Schematic illustration of Cu and CFRTP joining during (a) normal FLJ with the tool at the center line of overlap zone, and (b) offset FLJ with tool offsetting 7 mm from center line toward the RS. Temperature measuring positions of A, C, R and E during normal FLJ, and O-A and O-R during offset FLJ are marked in (a) and (b), respectively.

Fig. 2. Typical macrostructural morphology of normal friction lap joint of Cu/CFRTP at 2000 rpm with tool located at center of overlap zone.

Fig. 3. Typical macrostructures of the opposing fractured surfaces of normal joints at 800, 1500 and 2000 rpm. Points of A, C, R and E on the fracture surface at 1500 rpm correspond to the positions for temperature measurement in Fig. 1.

Fig. 4. Temperature measurements at different positions of normal FLJ CFRTP-Cu joint at 1500 rpm. Black, red, blue and green curves stand for the temperature on points C, A, R and E, respectively in Figs. 1a and Fig. 3.

Fig. 5. Typical macrostructures of the opposing fractured surfaces of offset joints at 800, 1500 and 2000 rpm. The points of O-A and O-R on the fracture surface at 1500 rpm were the positions used for temperature measurement.

Fig. 6. (a) Variation of TSF with rotation rate for the normal and offset FLJ joints, (b) estimated residual CFRTP area on Cu surface for the normal and offset FLJ joints, (c) temperature measurement at edge of tool on AS and RS (Points O-A and O-R in Figs. 1b and 5) for offset FLJ joint at 1500 rpm, and (d) the increasing efficiency of TSF and residual CFRTP area for offset FLJ joint.

Fig. 7. Macrostructural cross sections of normal and offset Cu/CFRTP joints at different rotation rates.

Fig. 8. Typical microstructure of Cu/CFRTP joints at 2000 rpm with different plunge depth for normal joints of (a) (c) (e) and for offset joints of (b) (d) (f): (a) (b) 0.3 mm, (c) (d) 0.6 mm, with (c) joint at edge inserted, and (e) (f) 0.9 mm.

Fig. 9. Bubble comparison of joints for (a)(c) normal FLJ and (b)(d) offset FLJ: typical cross-section of FLJ Cu/CFRTP joint with (a) normal and (b) offset joints for 1500 rpm, fracture surfaces on the CFRTP side of (c) normal and (d) offset joints for 2000 rpm.

Fig. 10. Bubble size distribution comparison in (a)(c)(e) normal FLJ joints and (b)(d)(f) offset FLJ joints: bubble distribution observed from fracture surfaces on the CFRTP side for (a) normal FLJ and (b) offset FLJ at 600 rpm, (c) normal FLJ and (d) offset FLJ at 2000 rpm, with detailed bubble distribution inserted, and bubble distribution observed from cross-section of FLJ Cu/CFRTP joint for (e) normal FLJ and (f) offset FLJ at 1500 rpm.

Table 1 Bubble statistical results for the normal and offset joints measured from fractured CFRTP surface.

	Rotation rate, rpm	Number	Total area, mm²	Fraction, %	Average size, mm²	Bubble Area on AS, mm²	Bubble Area on RS, mm²
Normal FLJ	600	839	18.97	34.80	0.0226	17.64	1.33
	800	221	3.19	5.85	0.0144	3.08	0.11
	1000	531	1.90	3.48	0.0036	1.85	0.05
	1500	2800	3.19	5.84	0.0011	2.97	0.22
	2000	605	16.33	29.95	0.0270	13.93	2.40
Offset FLJ	600	15	0.015	0.027	0.0010	0	0.015
Offset FLJ	2000	516	3.06	5.57	0.0059	1.77	1.29

Table 2 Bubble statistical results measured from cross sections of normal and offset Cu/CFRTP joints.

Rotation rate, rpm	Normal FLJ			Offset FLJ
Rotation rate, rpm	Number	Total area (mm²)	Average size (mm²)	Number	Total area (mm²)	Average size (mm²)
600	46	0.23	0.0050	12	0.015	0.0012
800	4	0.06	0.0150	9	0.020	0.0022
1000	129	0.46	0.0036	37	0.190	0.0051
1500	601	0.80	0.0013	393	0.617	0.0016
2000	362	10.70	0.0296	69	0.150	0.0022

Fig. 11. Vickers hardness of CFRTP side near the interface of Cu/CFRTP joints at 2000 rpm for (a) normal, and (b) offset FLJ.

Fig. 12. Typical microstructure at CFRTP side with (a) low hardness on edge of the AS, and (b) high hardness near tool center line for normal FLJ joint at 2000 rpm.

References

[1]	C. Alia, J.M. Arenas, J.C. Suarez, R. Ocana, J.J. Narbon, J. Adhes. Sci. Technol., 27(2013), pp. 2480-2494
[2]	A. Fink, P.P. Camanho, J.M. Andres, E. Pfeiffer, A. Obst, Compos. Sci. Technol., 70(2010), pp. 305-317
[3]	K. Nagatsuka, S. Yoshida, A. Tsuchiya, K. Nakata, Compos. Part B, 73(2015), pp. 82-88
[4]	S. Katayama, Y. Kawahito, Scripta Mater., 59(2008), pp. 1247-1250
[5]	K.W. Jung, Y. Kawahito, M. Takahashi, S. Katayama, Mater. Des., 47(2013), pp. 179-188
[6]	S.T. Amancio, C. Bueno, J.F. dos Santos, N. Huber, E. Hage, Mater. Sci. Eng. A, 528(2011), pp. 3841-3848
[7]	G. Wagner, F. Balle, D. Eifler, Adv. Eng. Mater., 15(2013), pp. 792-803
[8]	C. Engelmann, L. Oster, A. Olowinsky, A. Gillner, V. Mamuschkin, D. Arntz, J. Laser Appl., 29 (2017)
[9]	M. Wahba, Y. Kawahito, S. Katayama, J. Mater. Process. Technol., 211(2011), pp. 1166-1174
[10]	K.W. Jung, Y. Kawahito, S. Katayama, Sci. Technol. Weld. Join., 16(2011), pp. 676-680
[11]	K.W. Jung, Y. Kawahito, M. Takahashi, S. Katayama, J. Laser Appl., 25(2013), p. 032003-6
[12]	F.C. Liu, K. Nakata, J. Liao, S. Hirota, H. Fukui, Sci. Technol. Weld. Join., 19(2014), pp. 578-587
[13]	F. Balle, S. Emrich, G. Wagner, D. Eifler, A. Brodyanski, M. Kopnarski, Adv. Eng. Mater., 15(2013), pp. 814-820
[14]	L.H. Wu, D. Wang, B.L. Xiao, Z.Y. Ma, Scripta Mater., 78-79(2014), pp. 17-20
[15]	R.S. Mishra, Z.Y. Ma, Mater. Sci. Eng. R, 50(2005), pp. 1-78
[16]	F.C. Liu, J. Liao, K. Nakata, Mater. Des., 54(2014), pp. 236-244
[17]	K. Nagatsuka, D. Kitagawa, H. Yamaoka, K. Nakata, ISIJ Int., 56(2016), pp. 1226-1231
[18]	K. Nagatsuka, H. Tanaka, B.L. Xiao, A. Tsuchiya, K. Nakata, Q. J. Jpn. Weld. Soc. (in Japanese), 33(2015), pp. 317-325
[19]	F. Yusof, Y. Mutoh, Y. Miyashita, Mater. Manuf. Technol., 129-131(2010), pp. 714-718
[20]	L.H. Wu, K. Nagatsuka, K. Nakata, J. Mater. Sci. Technol., 34 (2018), pp. 192-197, 10.1016/j.jmst.2017.10.019
[21]	C.W. Chan, G.C. Smith, Mater. Des., 103(2016), pp. 278-292
[22]	Y. Farazila, Y. Miyashita, W. Hua, Y. Mutoh, Y. Otsuka, J. Laser Micro Nanoeng., 6(2011), pp. 69-74