J. Mater. Sci. Technol. ›› 2020, Vol. 41 ›› Issue (0): 105-116.DOI: 10.1016/j.jmst.2019.10.005

• Research Article • Previous Articles     Next Articles

Microstructure and mechanical properties of double-side friction stir welded 6082Al ultra-thick plates

C. Yangab, J.F. Zhanga, G.N. Maa, L.H. Wua, X.M. Zhangc, G.Z. Hec, P. Xuea*(), D.R. Nia*(), B.L. Xiaoa, K.S. Wangd, Z.Y. Maa   

  1. aShenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
    bSchool of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
    cCRRC Changchun Railway Vehicles Co., Ltd., Changchun 130062, China
    dSchool of Metallurgical Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China
  • Received:2019-06-26 Revised:2019-08-22 Accepted:2019-10-22 Online:2020-03-15 Published:2020-04-10
  • Contact: Xue P.,Ni D.R.

Abstract:

In the present work, 80 mm thick 6082Al alloy plates were successfully double-side welded by friction stir welding (FSW). The relationship between the microstructures and mechanical properties was built for the double-side FSW butt joint with more attention paid to the local characteristic zones. It was shown that a phenomenon of microstructural inhomogeneity existed in the nugget zone (NZ) through the thickness direction. The grain size presented an obvious gradient distribution from the top to the bottom for each single-pass weld, and the microhardness values decreased from both surfaces to the middle of the NZ. The lowest hardness zone (LHZ) exhibited a “hyperbolical”-shaped distribution extending to the middle of the NZ. Similar tensile properties were obtained in the three sliced specimens of the FSW joint, and the joint coefficient reached about 70% which achieved the same level as the conventional FSW Al alloy joints. Finite element modeling proved that the “hyperbolical”-shaped heat affected zone (HAZ) was beneficial to resisting the strain concentration in the middle layer specimen which helped to increase the tensile strength. Based on the analysis of the hardness contour map, tensile property and microstructural evolution of the joints, an Isothermal Softening Layer (ISL) model was proposed and established, which may have a helpful guidance for the optimization on the FSW of ultra-thick Al alloy plates.

Key words: Ultra-thick aluminum alloy plates, Double-side friction stir welding, Finite element model, Microstructural inhomogeneity, Mechanical properties