Microstructure of friction stir welded single crystal pure iron

Abstract

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 5μm 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 <111>orientation. The <111>common axis was parallel to the transverse direction (TD) at the center of the joint, and the <111>axis rotated around the ND with moving away from the joint center. At the edge of the stir zone, the <111>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.