Refill friction stir spot welding of 5083-O aluminum alloy

doi:10.1016/j.jmst.2017.02.011

Abstract

Abstract:

In this work, refill friction stir spot welding (RFSSW) was used to weld 2 mm-thick 5083-O alloy. The Box-Behnken experimental design was used to investigate the effect of welding parameters on the joint lap shear property. Results showed that a surface indentation of 0.3 mm effectively eliminated the welding defects. Microhardness of the stir zone (SZ) was higher than that of the base material (BM) and the hardness decreased with increasing the heat input during welding. The optimum failure load of 7.72 kN was obtained when using rotating speed of 2300 rpm, plunge depth of 2.4 mm and refilling time of 3.5 s. Three fracture modes were obtained during the lap shear test and all were affected by the hook defect.

Key words: Refill friction stir spot welding, Keyhole, Secondary phases, Microhardness, Lap shear failure load

Zhiwu Xu, Zhengwei Li, Shude Ji, Liguo Zhang. Refill friction stir spot welding of 5083-O aluminum alloy[J]. J. Mater. Sci. Technol., 2018, 34(5): 878-885.

Figures/Tables 10

Table 1 Welding parameters and their levels.

Parameters	Symbol	Level Low (-1)	Level Middle (0)	Level High (1)
Rotating speed (rpm)	RS	2300	2500	2700
Plunge depth (mm)	PD	2.2	2.3	2.4
Refilling time (s)	RT	1.5	2.5	3.5

Table 2 Box-Behnken design matrix and experimental results.

No.	RS (rpm)	PD (mm)	RT (s)	Failure load (kN)
1	2500	2.3	2.5	6.99
2	2300	2.3	3.5	7.17
3	2700	2.3	3.5	5.0
4	2300	2.3	1.5	6.5
5	2500	2.2	3.5	6.4
6	2500	2.4	3.5	7.36
7	2500	2.4	1.5	7.4
8	2700	2.2	2.5	6.3
9	2500	2.2	1.5	6.75
10	2300	2.4	2.5	7.3
11	2500	2.3	2.5	7.1
12	2500	2.3	2.5	6.8
13	2500	2.3	2.5	6.95
14	2700	2.3	1.5	6.8
15	2500	2.3	2.5	7.38
16	2300	2.2	2.5	7
17	2700	2.4	2.5	5.7

Fig. 1. Cross section of the RFSSW joint: (a) joint without surface indentation, (b) incomplete refilling, (c) void, (d) joint with a 0.3 mm surface indentation, (e) magnified view of the indentation and (f) hook.

Fig. 2. Material flow behavior during the RFSSW process: (a) refilling process, (b) without indentation and (c) with a 0.3 mm indentation.

Fig. 3. BM and secondary phases: (a) SEM photograph of the BM, (b) Al3Mg2 phase, (c) and (d) Al6(MnFe) phase.

Fig. 4. Secondary phases at different regions: (a) HAZ, (b) TMAZ and (c) SAZ and (d) PAZ.

Fig. 5. Microhardness of the RFSSW joint: (a) upper sheet and (b) lower sheet using different rotating speeds, (c) upper sheet and (d) lower sheet using different refilling time.

Table 3 Analysis of the variable table.

Source	Sum of Squares	df	Mean square	F Value	p-value prob > F
Model	5.77	9	0.64	6.11	0.0131
RS	2.17	1	2.17	20.70	0.0026
PD	0.21	1	0.21	2.04	0.1690
RT	0.29	1	0.29	2.75	0.1412
RS × PD	1.20	1	0.20	1.93	0.2075
RS × RT	1.53	1	1.53	14.53	0.0066
PD × RT	0.024	1	0.024	0.23	0.6470
RS²	1.23	1	1.23	11.67	0.0112
PD²	0.021	1	0.021	0.20	0.6687
RT²	0.079	1	0.079	0.75	0.4144
Residual	0.73	7	0.10
Lack of fit	0.55	3	0.18	3.90	0.1109
Pure error	0.19	4	0.047
Cor total	6.51	16

Fig. 6. Response surface graphs: (a) plunge depth of 2.3 mm, (b) refilling time of 2.5 s and (c) rotating speed of 2500 rpm.

Fig. 7. Fracture modes of the RFSSW joint: (a) joint morphology, (b) hook and (c) schematic of the shear fracture mode, (d) joint morphology, (e) hook and (f) schematic of the shear-plug fracture mode, (g) joint morphology, (h) hook and (i) schematic of the plug fracture mode.

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