Grain Orientation and Texture Evolution in Pure Titanium Lap Joint Produced by Friction Stir Welding

Abstract

Pure titanium lap joints were produced by friction stir welding, and the grain orientation and texture evolution were investigated as well as the mechanical property of the lap joint. The grain orientation changes obviously after welding, and the strong P₁ texture formed in the stir zone suggests that the metal flow can be characterized by a simple shear deformation. The shear plane in the center and bottom parts of the stir zone is shown to be a spherical crown surface, which is nearly similar to the bottom shape of the probe. The vertical flow of stirred metal is slight and it may be a reason why the welding condition is narrow. The hardness in the stir zone is distinctly higher than that in the base metal due to the grain refinement after FSW, and the shear tensile strength is so high that the fracture happens at the base metal, resulting from both the hardness increase in the stir zone and the sufficient width of lap zone.