Effects of post-weld heat treatment on microstructures and mechanical properties of AA7204-T4 aluminum alloy FSW joint
Yun-lai DENG1,2, Shu-hao DENG1, Ling-ying YE1,*(), Sen LIN1, Lin SUN3, Hua JI2
1 School of Materials Science and Engineering, Central South University, Changsha 410083, China 2 Light Alloy Research Institute, Central South University, Changsha 410083, China 3 China Railway Rolling Stock Corporation Qingdao Sifang Co., Ltd., Qingdao 266000, Shandong, China
AA7204-T4 aluminum alloy plates were welded by friction stir welding(FSW), and the effect of post-weld heat treatment on the microstructure and mechanical properties of the FSW joints were studied. The results show that the average grain size(AGS) and recrystallization fraction of nugget zone(NZ) are 4.7 μm and 81.9% in as-welded(AW) treatment, 4.8 μm and 82.4% under the post-weld artificial aging(AA) treatment, 5.9 μm and 86.5% under the heat treatment of solid solution followed by artificial aging(SAA), respectively. The grain structure of NZ is not obviously affected by AA treatment, and the AGS and recrystallization fraction of NZ increase by 25.5% and 5.6% under SAA treatment. The ultimate tensile strength(UTS) of the FSW joints are 296.6, 318.2, 357.4 MPa under the heat treatments of AW, AA and SAA, respectively. The improvement of the mechanical properties of FSW joints is limited by AA treatment, while that can be effectively improved by SAA treatment which leads to the welding coefficient reaching 92.0%. Additionally, the microcracks tend to generate on the "S" line under the effect of water quenching after solid solution, which would lead to the fracture location at this zone and the serious decrease of the elongation.
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