Microstructure of friction stir welded single crystal pure iron

The microstructure of a pure iron joint fabricated by friction stir welding (FSW) was investigated. The base metal was a pure iron sheet with a single crystal fabricated by the recrystallization method. [100] and [011] in the base metal were parallel to the normal direction (ND) and the welding direction (WD), respectively. The stir zone of the joint contained fine grains of 3 to 5 μm size. The measurement of the electron back scattering diffraction pattern (EBSD) of the stir zone clarified a significant texture. Although the microstructure was subdivided into fine grains by the high angle random grain boundaries with high density, these fine grains had a common rotation axis having  orientation. The  common axis was parallel to the transverse direction (TD) at the center of the joint, and the  axis rotated around the ND with moving away from the joint center. At the edge of the stir zone, the  common axis became parallel to the WD. The formation mechanism of this texture will be discussed along with the plastic flow during the FSW process.