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The Influence of Pre- and Post-Heat Treatment on Mechanical Properties and Microstructures in Friction Stir Welding of Dissimilar Age-Hardenable Aluminum Alloys

by Yang Jia 1, Sicong Lin 1, Jizi Liu 1,2,*, Yonggui Qin 1 and Kehong Wang 1,*
1
School of Materials Science and Engineering/Herbert Gleiter Institute of Nanoscience, Nanjing University of Science and Technology, Nanjing 210094, China
2
State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, Hunan University, Changsha 410082, China
*
Authors to whom correspondence should be addressed.
Metals 2019, 9(11), 1162; https://doi.org/10.3390/met9111162
Received: 27 September 2019 / Revised: 23 October 2019 / Accepted: 25 October 2019 / Published: 28 October 2019
(This article belongs to the Special Issue Characterization of Welded Joints)
An Al-Mg-Si alloy 6061 and an Al-Zn-Mg alloy 7A52 were joined by friction stir welding successfully. Pre- and post- heat treatment were employed to improve the strength of the weld. The results show a best weld joint with the lowest hardness of 100 HV in 6061 matrix, being achieved by post-solid-solution and subsequent two-stage artificial aging for the whole weld joint of the 7A52 and 6061 solid solution. Under this condition, the weld nugget zone (WNZ) is stronger than 6061 matrix but it has lower hardness than 7A52 matrix. The hardness of WNZ is contributed by the combination of η′ and L precipitates, dynamically changes along with the ratios between the number of η′ and L precipitates. The higher the number density of η′ precipitates, the hardness of WNZ is closer to that of the 7A52 matrix. Otherwise, the higher number density of L precipitates, the hardness of WNZ is closer to that of 6061 matrix. The coexistence of η′ and L precipitates is a direct result from the mixture of 7A52 and 6061 alloys achieved by stirring. Precipitates identification and composition analysis reveal a dynamic WNZ with constituent transition in hardness and composition. View Full-Text
Keywords: friction stir welding; aluminum alloy; heterogeneity; mechanical; microstructure friction stir welding; aluminum alloy; heterogeneity; mechanical; microstructure
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Jia, Y.; Lin, S.; Liu, J.; Qin, Y.; Wang, K. The Influence of Pre- and Post-Heat Treatment on Mechanical Properties and Microstructures in Friction Stir Welding of Dissimilar Age-Hardenable Aluminum Alloys. Metals 2019, 9, 1162.

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