Effect of rotation and traverse rate on texture and phase evolution during friction stir welding of dissimilar titanium alloys.

Friction Stir Welding (FSW) research thus far consists of various titanium alloys, with a predominant emphasis on Ti-6Al-4V, a workhorse of the aerospace industry. However, limited studies exist on the texture evolution of FSWed dissimilar titanium alloys. This study is among the first to analyze the texture of FSWed dissimilar titanium alloys, examining 5-mm-thick sheets of a near-α titanium alloy (Ti-6242 standard grain) and an α+β titanium alloy (Ti-54M). The FSW was conducted using a parametric matrix of three rotational speeds (225, 275, and 325 rpm) and three traverse speeds (100, 125, and 150 (mm/min)). A detailed microstructural analysis was conducted for specific combinations of rotational and traverse speeds to assess phase evolution and texture development. The study examined crystallographic texture evolution by analyzing specific planes, namely (100)_α, (002)_α, (110)_β, (101)_α, and (102)_α, to determine the effects of processing conditions on material anisotropy. In particular, the primary texture components, (101)_α and (002)_α, were assessed for their intensity and orientation under different welding conditions. Results revealed that, except at the lowest rotational speed (225 rpm), weld nugget predominantly exhibited lamellar (α+β) structures. The aspect ratios of the α laths varied with rotational speed, indicating its significant influence on microstructural characteristics. At 225 rpm, microstructure was primarily composed of equiaxed α grains, suggesting that lower rotational speeds create distinct thermal and mechanical environments that influence grain morphology. Traverse speed also played a crucial role in texture development and phase distribution, particularly in the formation of adiabatic shear bands within the weld nugget. These shear bands, indicative of localized plastic deformation, contributed to the observed inhomogeneity in texture and phase distribution. The presence of such bands at different traverse speeds underscores the complex interaction between thermal and mechanical forces during FSW.