Effects of Post-Weld Heat Treatment on Microstructure and Mechanical Properties of Al-12.7Si-0.7Mg Alloy Welded Joints by GMAW

doi:10.1007/s40195-014-0052-4

Abstract

Abstract:

In this study, 3-mm-thick hot-extruded plates of Al-12.7Si-0.7Mg alloy were used to fabricate the joints welded by gas metal arc welding. Effects of the post-weld heat treatment include solid solution treatment, water quenching, and artificial aging treatment on the microstructure, and mechanical properties of the weld joints have been investigated. Results showed that the welded joints after solid solution and artificial aging exhibited the increases in yield strength of 166 MPa and ultimate tensile strength of 148 MPa, respectively. Based on the microstructural observations, the associated mechanisms were discussed.

Key words: Al–Si alloy, Welded joint, Post-weld heat treatment (PWHT), Microstructure, Mechanical property

Dong Wang, Changshu He, Hao Wang, Xiang Zhao, Liang Zuo. Effects of Post-Weld Heat Treatment on Microstructure and Mechanical Properties of Al-12.7Si-0.7Mg Alloy Welded Joints by GMAW[J]. Acta Metallurgica Sinica (English Letters), 2014, 27(2): 245-252.

Figures/Tables 10

Table 1 Welding parameters

Current (A)	Voltage (V)	Feeding speed (cm/min)	Travel speed (cm/min)	Argon flow rate (L/min)
105	19	450	55	15

Fig. 1 Micro-hardness distribution in the as-welded and PWHT joints

Table 2 Mechanical properties of weld joints and base material after different treatments

Treatment	Sample	UTS (MPa)	YS (MPa)	Elongation (%)
Hot extruded	Weld	189	106	8.96
Hot extruded	BM	201	108	11.37
Aged at 180 °C for 1 h	Weld	310	215	9.12
Aged at 180 °C for 1 h	BM	366	287	10.93
Aged at 180 °C for 2 h	Weld	308	210	7.28
Aged at 180 °C for 2 h	BM	384	341	7.33
Aged at 180 °C for 3 h	Weld	337	272	4.80
Aged at 180 °C for 3 h	BM	385	343	7.05

Fig. 2 Macro morphology of fractured tensile tested specimens: a the as-welded, b PWHT (540 °C/1.5 h + 180 °C/3 h)

Fig. 3 SEM fractographs of tensile tested specimens: a the as-welded, b PWHT

Fig. 4 Micrographs of side views of the fractured tensile samples: a the as-welded, b PWHT

Fig. 5 Microstructures of the as-welded joint: a low-magnification micrograph, b BM, c HAZ, d FZ, e WZ center

Fig. 6 SEM micrograph and EDS results of the intermetallic phases in the weld zone

Fig. 7 Microstructures of PWHT (540 °C/1.5 h + 180 °C/3 h) joint: a BM, b HAZ, c FZ, d WZ center

Fig. 8 TEM bright field images and the [001] selected area diffraction patterns obtained from a WZ of the as-welded joint, b HAZ of the as-welded joint, c WZ of PWHT (540 °C/90 min + 180 °C/3 h) joint, d HAZ of PWHT (540 °C/1.5 h + 180 °C/3 h) joint, respectively

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