Effect of Post Aging on Mechanical Properties of Friction Stir Welded 7046 Aluminum Alloy

doi:10.11901/1005.3093.2020.227

Chinese Journal of Materials Research

2021, Vol. 35

Issue (7): 543-552 DOI: 10.11901/1005.3093.2020.227

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Effect of Post Aging on Mechanical Properties of Friction Stir Welded 7046 Aluminum Alloy

LIAO Zexin¹^,², LI Chengbo¹^,²^,³, LIU Shengdan¹^,²^,⁴(

), TANG Jianguo¹^,²^,⁴, HUANG Chuanyan³, ZHU Xianyan³

^1.School of Materials Science and Engineering, Central South University, Changsha 410083, China
^2.Key Laboratory of Nonferrous Metal Materials Science and Engineering, Ministry of Education, Central South University, Changsha 410083, China
^3.Guangdong Hoshion Industrial Aluminum Co. Ltd. , Zhongshan 528463, China
^4.Nonferrous Metal Oriented Advanced Structural Materials and Manufacturing Cooperative Innovation Center, Central South University, Changsha 410083, China

Cite this article:

LIAO Zexin, LI Chengbo, LIU Shengdan, TANG Jianguo, HUANG Chuanyan, ZHU Xianyan. Effect of Post Aging on Mechanical Properties of Friction Stir Welded 7046 Aluminum Alloy. Chinese Journal of Materials Research, 2021, 35(7): 543-552.

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Abstract

Extruded sheets of 7046 aluminum alloy of 3.5 mm in thickness were subjected to friction stir welding (FSW) and then post aging treatment. The hardness profile of the FSW joint exhibits a "W" shape and the ultimate tensile strength is 406.5 MPa with a welding coefficient of 0.8. During tensile test fracture appears at the minimum hardness zone, which is the transition area between the heat affected zone (HAZ) and the thermal-mechanically affected zone (TMAZ) on the retreating side. There are a lot of dimples on the fracture surface. After aging at 120℃ for 24 h there is little change in the hardness of the base metal (BM) but the hardness of the HAZ, TMAZ and nugget zone (NZ) increase apparently, which is more or less the same as that of the BM. The ultimate tensile strength increases significantly up to about 490MPa with the welding coefficient increasing to about 0.96. Fracture appears at the NZ and there are a lot of intergranular cracks on the fracture surface. After aging, the GPI zones within grains of the FSW joint transform into η' metastable phase with better strengthening effect, leading to higher hardness and strength. η phase tends to be more continuous at grain boundaries and there is a higher volume fraction of precipitates free zones near grain boundaries in the NZ than other regions, therefore, fracture tends to occur in the NZ during tensile test.

Key words: metallic materials 7046 aluminum alloy friction stir welding post weld aging microstructure mechanical properties

Received: 13 June 2020

ZTFLH:

TG457.14

Fund: National Key Research and Development Program of China(2016YFB0300901);Key Project of Science and Technology of Zhongshan Bureau of Guangdong Province(2016A1001)

About author: LIU Shengdan, Tel: (0731)88830265, E-mail: lsd_csu@csu.edu.cn

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	Zexin LIAO
	Chengbo LI
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	Jianguo TANG
	Chuanyan HUANG
	Xianyan ZHU

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https://www.cjmr.org/EN/10.11901/1005.3093.2020.227 OR https://www.cjmr.org/EN/Y2021/V35/I7/543

Table 1 Chemical compositions of 7046 aluminum alloy (mass fraction, %)

Table 2 Friction stir welding parameters

Fig.1 Schematic of hardness tests and tensile samples cut from the FSW joint (ED: extrusion direction, TD: transverse direction, ND: normal direction)

Fig.2 Macroscopic morphology of transverse cross section of FSW joint

Fig.3 Optical images of BM、HAZ、TMAZ zone of FSW joint (a) position a in Fig.2, (b) position b in Fig.2, (c) position c in Fig.2, (d) position d in Fig.2

Fig.4 Optical images of NZ zone and SAZ zone of FSW joint (a) position e in Fig.2, (b) position f in Fig.2, (c) position g in Fig.2

Fig.5 TEM images and SADP of BM zone、HAZ zone and NZ zone of FSW joint (a, b) BM zone, (c, d) HAZ zone, (e, f) NZ zone, (g) Near <110>_Al SADP of BM zone, (h) As a representative, <100>_Al SADP of HAZ zone is given

Table 3 Size, spacing of precipitates and PFZ width at the grain boundary of different samples

Fig.6 TEM images and SADP of BM zone、HAZ zone and NZ zone of AG-FSW joint (a, b) BM zone; (c, d) HAZ; zone; (e, f) NZ zone; (g) As a representative, near <110>_Al SADP of NZ zone is given

Fig.7 Hardness profiles of FSW and AG-FSW joint

Table 4 Tensile properties of BM and FSW joint at room temperature

Fig.8 Optical images of fracture surface of FSW joint after tensile test (a) FSW joint, (b) AG-FSW joint

Fig.9 SEM images of fracture surface of FSW joint after tensile test (a) FSW joint, (b) AG-FSW joint

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