Influence of texture on strain localization in stir zone of friction stir welded titanium

• Strong texture in the SZ induced special local deformation during tensile test.
• A distinctive plastic deformation initially occurred in the high hardness stir zone.
• Very high Schmid factors for prismatic slip in the stir zone was determined.
• Higher thickness strain than width strain occurred in the stir zone.

Friction stir welding has a great advantage in welding of titanium because it can avoid solidification problems and generate fine grain structure in the weld region. However, the strong texture formed in the weld region may affect the mechanical properties and deformation behavior of the joints. The present work seeks to understand the comprehensive effect of grain structure and texture on the local deformation behavior in the weld region. It was found that although the weld region had a finer grain structure and a higher hardness than the base material (BM), a distinctive plastic deformation extensively occurred within the weld region during the initial tensile deformation stage because the Schmid factor for prismatic slip in the weld region is much higher than that in the BM. At high strain, the difference of Schmid factor for prismatic slip deformation between the weld region and the BM was significantly reduced and the effect of grain size became more significant than Schmid factor. Therefore, the local deformation in the weld region was restrained, and the tensile sample failed in the BM finally.