Abstract
After friction stir processing (FSP), fine equiaxed α-Al grains formed in the weld nugget (WN) of 6063 Al alloy, and their size increased with increasing tool rotation speed in the range of 300–700 rpm. The grain sizes in the bottom zones were smaller than those in the upper zones in the WN, and two-pass FSP led to a larger grain size than single-pass FSP. Tunnel defects can be observed in the thermomechanically affected zone (TMAZ) for a low tool rotation speed of 300 rpm. When the rotation speed exceeds 700 rpm, a good combination interface can form between the WN and the TMAZ. Electron backscatter diffraction (EBSD) results showed that the fraction of the high-angle grain boundary (HAB) was obviously increased after FSP in the WN. The alloys exhibited a more concentrated distribution and higher densities. Transmission electron microscopy (TEM) analysis results showed that the densities of needle-shaped precipitates were reduced in the WN. Some high-density dislocation pile-ups formed at some grains. The ultimate tensile strengths (UTSs) were lower than that of the base material (BM) at lower tool rotation speeds for both single- and two-pass FSP. With increasing speed, the UTSs increased gradually and then became higher than that of the BM. The strain values were all lower than that of the BM.
Published Version
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