Impact of shoulder concavity on non-tool-tilt friction stir welding of 5052 aluminum alloy.

In regard to the non-tool-tilt friction stir welding (NTT-FSW) process, the shoulder concavity has significant effects on the control of heat generation and material flow, and thus is an important geometrical feature for the tool design. In this paper, three types of shoulder concavity angles (SCAs), i.e., 0°, 5°, and 10°, were selected to explore the impact of SCA on the NTT-FSW of 5052 aluminum alloy. The results indicate that the increase of SCA lowers the tool axial force, reduces the nugget width, and weakens the band structure in the nugget. A weakening of shoulder thermal effect occurs from 0° to 5° SCA, leading to an improvement of the structure-property of the NTT-FSW joint. Further increasing the SCA to 10° causes the generation of the secondary sliding frictional heat at the interface between the shoulder-driven material and the base material, and thus the shoulder thermal effect does not show a continuous weakening trend as expected but becomes stronger instead, resulting in the deterioration of the microstructure evolution and the degradation of the tensile strength of NTT-FSW joint. [ABSTRACT FROM AUTHOR]