Microstructure and Properties of 2A14-T4 Aluminum Alloy T Joint by SSFSW
YANG Haifeng1,2, ZHAO Hongyun1,2, XU Xinxin2, SUN Guangda1,2, ZHOU Li1,2, ZHAO Huihui3, LIU Huijie1
1 State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001, China 2 Key Laboratory of Special Welding Technology Shandong Province, Harbin Institute of Technology(Weihai), Weihai 264209, China 3 Shanghai Aerospace Equipments Manufacturer Co., Ltd., Shanghai 200245, China
Abstract: 2A14-T4 aluminum alloy T joint with a thickness of 8.5 mm was connected by stationary shoulder friction stir welding (SSFSW). The weld formability, microstructures and mechanical properties of T joint were studied. The results showed that the smooth surface with small flash could be obtained and no defects were found in SSFSW welds. The cross section morphology of SSFSW-T joint presents an “open dumbbell” with both ends wide and middle narrow. Recrystallization occurred and the grain size decreased obviously in the weld nugget zone (WNZ). The average grain size was the largest in the second weld nugget zone (WNZ2), followed by the weld nugget overlap zone (WNOZ) and the smallest grains were in the first weld nugget zone (WNZ1). The recrystallization mechanism in WNZ is mainly geometric dynamic recrystallization (GDRX) and partially continuous dynamic recrystallization (CDRX). The thermo-mechanically affected zone (TMAZ) is narrow and the grains were elongated. And the grain coarsening occurred in heat affected zone (HAZ). During the welding process, the second phase particles were precipitated and coarsened, resulting in the decreasing hardness of WNZ. The fracture locations of T joint bottom plate and reinforcement plate were in the lowest hardness zone located in the borderline between TMAZ and HAZ and stress concentration locations in tensile test, respectively. Tear ridge and deformation dimples of different sizes could be observed in the fracture surface. And the second phase particles appear in the dimples, showing the characteristics of ductile fracture.
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2021, Vol. 35 
