Effect of Sheet Configuration on Microstructure and Mechanical Behaviors of Dissimilar Al-Mg-Si/Al-Zn-Mg Aluminum Alloys Friction Stir Welding Joints

doi:10.1016/j.jmst.2016.10.011

Abstract

Abstract:

Friction stir welding (FSW) was used to weld dissimilar Al-Mg-Si/Al-Zn-Mg aluminum alloys in this work. Influences of sheet configuration on microstructure and mechanical properties of the joints were mainly discussed. Results showed that rather different joint cross sections were obtained when using different sheet configurations. Coarser β' phases can be observed at the heat affected zone (HAZ) of the Al-Mg-Si alloy side, which was the main factor affecting the tensile properties and the fatigue properties. Tensile strengths of the dissimilar Al-Mg-Si/Al-Zn-Mg joints using both configurations were higher than that of the Al-Mg-Si FSW joint. When the Al-Zn-Mg alloy was located at the advancing side (AS), the joints owned better fatigue properties due to the bridging effect of the big secondary phase particles.

Key words: Friction stir welding, Dissimilar aluminum alloys, Microstructure, Tensile properties, Fatigue life

Yan Zhongjie,Liu Xuesong,Fang Hongyuan. Effect of Sheet Configuration on Microstructure and Mechanical Behaviors of Dissimilar Al-Mg-Si/Al-Zn-Mg Aluminum Alloys Friction Stir Welding Joints[J]. J. Mater. Sci. Technol., 2016, 32(12): 1378-1385.

Figures/Tables 16

Table 1. Nominal chemical compositions of the BM (wt%)

BM	Si	Fe	Cu	Mn	Mg	Zn	Ti	Cr	Al
Al-Mg-Si	0.4-0.9	≤0.35	≤0.35	≤0.50	0.4-0.8	≤0.25	≤0.10	≤0.30	Bal.
Al-Zn-Mg	≤0.30	≤0.30	≤0.20	0.2-0.7	1.0-2.0	4.0-5.0	≤0.20	≤0.30	Bal.

Table 2. Mechanical properties of the BM

BM	Tensile strength (MPa)	Yield strength (MPa)	Elongation (%)
Al-Mg-Si	284	241	25
Al-Zn-Mg	368	256	19.5

Fig. 1. Dimensions of the test specimens: (a) tensile specimen, (b) fatigue specimen and (c) bending specimen.

Fig. 2. Cross sections of the joints: (a) Al-Zn-Mg-AS joint, (b) Al-Mg-Si-AS joint.

Fig. 3. Al-Zn-Mg alloy BM: (a) OM, (b) SEM and (c) EDS results of the secondary phase particles; Al-Mg-Si alloy BM: (d) OM and (e) SEM and (f) EDS results of the secondary phase particles.

Fig. 4. Microstructures of the joints: (a) HAZ, (b) TMAZ and (c) SZ of the Al-Zn-Mg side on the Al-Zn-Mg-AS joint; (d) HAZ, (e) TMAZ and (f) SZ of the Al-Mg-Si side on the Al-Mg-Si-AS joint.

Fig. 5. Bonding interfaces at the SZ center of the joints: (a) the Al-Zn-Mg-AS joint and (c) its EDS analysis result; (b) the Al-Mg-Si-AS joint and (d) its EDS analysis result.

Fig. 6. Micro-hardness of the joints using different configurations: (a) hardness testing points, (b) the Al-Zn-Mg-AS joint and (c) the Al-Mg-Si-AS joint.

Fig. 7. Tensile properties of the FSW joints.

Fig. 8. Fracture positions of the joints: (a) the Al-Zn-Mg-AS joint and (b) the Al-Mg-Si-AS joint.

Fig. 9. Specimens after the bending test: (a) side view and (b) front view of the Al-Zn-Mg-AS specimens, (c) side view and (d) front view of the Al-Mg-Si-AS specimens.

Table 3. Fatigue properties of the FSW joint using different configurations

Joint	Stress (MPa)	Fatigue life
Al-Zn-Mg-AS joint	160	463,652
	150	531,128
	140	1,972,459
	120	4,119,358
	110	8,644,824
	100	>10⁷
Al-Mg-Si-AS joint	160	318,265
	150	729,652
	140	1,241,895
	120	1,471,565
	110	2,319,586
	100	6,574,812

Fig. 10. TEM photographs of precipitated phase particles at the BM of the Al-Mg-Si alloy: (a) precipitated phase particles and its magnified view (b), the EDS results of the point A (c) and B (d).

Fig. 11. TEM photographs of precipitated phase particles at the HAZ of the Al-Mg-Si alloy: (a) Al-Zn-Mg-AS joint and (b) Al-Mg-Si-AS joint.

Fig. 12. TEM photographs of precipitated phase particles at the TMAZ of the Al-Mg-Si alloy: (a) Al-Zn-Mg-AS joint and (b) Al-Mg-Si-AS joint.

Fig. 13. TEM photographs of precipitated phase particles at the SZ of the Al-Mg-Si alloy: (a) Al-Mg-Si-RS joint and (b) Al-Mg-Si-AS joint, the EDS results of the point A (c) and B (d) in (b).

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