Friction Stir Spot Welding process (FSSW) is a distinct variant of Friction Stir Welding (FSW) that has been proven to be effective in various industrial applications. In this paper, FSSW joint on overlapped 3-mm-thick AA2017-T351 sheets aluminum alloy, welded with 1500 rpm as tool rotational speed, 5 mm/min plunge rate, 15 s as dwell time and 5.2 mm plunge depth, was investigated. Microstructural observations, microhardness measurements, tensile/shear tests and fractography of the spot weld were conducted. Results showed that thermal evolution and plastic deformation had a remarkable effect on the grain structure (the hardness is 124 HV at BM, decreases to 109 HV at HAZ/TMAZ and reaches 135 HV at SZ) and size (from typically 15 µm in BM to mainly under 2 µm in the SZ). The fully bonded region width was nearly 150 µm and the maximum tensile/shear load was 2.6 kN. Two types of fracture modes were analyzed following the tensile shear test, namely pull-out nugget and shear failure fracture mode.
Jemal et al. (Tue,) studied this question.