J. Mater. Sci. Technol. ›› 2018, Vol. 34 ›› Issue (1): 173-184.DOI: 10.1016/j.jmst.2017.05.015

Special Issue: FSW-and-FSP-articles 2018

• Orginal Article • Previous Articles     Next Articles

Comparative study on local and global mechanical properties of bobbin tool and conventional friction stir welded 7085-T7452 aluminum thick plate

Weifeng Xua*(), Yuxuan Luoa, Wei Zhanga, Mingwang Fub   

  1. a State Key Laboratory of Solidification Processing, Shaanxi Key Laboratory of Friction Welding Technologies, Northwestern Polytechnical University, Xi'an 710072, Shaanxi, China
    b Department of Mechanical Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China
  • Received:2017-02-20 Revised:2017-04-17 Accepted:2017-05-08 Online:2018-01-20 Published:2018-02-09
  • Contact: Xu Weifeng

Abstract:

7085-T7452 plates with a thickness of 12 mm were welded by conventional single side and bobbin tool friction stir welding (SS-FSW and BB-FSW, respectively) at different welding parameters. The temperature distribution, microstructure evolution and mechanical properties of joints along the thickness direction were investigated, and digital image correlation (DIC) was utilized to evaluate quantitatively the deformation of different zones during tensile tests. The results indicated that heat-affected zone (HAZ), the local softening region, was responsible for the early plastic deformation and also the fracture location for SS-FSW samples, while a rapid fracture was observed in weld nugget zone (WNZ) before yield behavior for all BB-FSW specimens. The ultimate tensile strength (UTS) of SS-FSW joints presented the highest value of 410 MPa, 82% of the base material, at a rotational speed of 300 rpm and welding speed of 60 mm/min, much higher than that of BB-FSW joints, with a joint efficiency of only 47%. This should be attributed to the Lazy S defect produced by a larger extent of heat input during the BB-FSW process. The whole joint exhibited a much higher elongation than the slices. Scanning electron microscopic (SEM) analysis of the fracture morphologies showed that joints failed through ductile fracture for SS-FSW and brittle fracture for BB-FSW.

Key words: Aluminum alloy, Friction stir welding, Bobbin tool, Temperature distribution, Microstructure, Mechanical properties