Thermal simulation and microstructural evolution of friction stir additive manufactured Ti-6Al-4V alloy

The morphology and microstructure of titanium alloys are significantly influenced by thermal input and temperature evolution during Friction Stir Additive Manufacturing (FSAM). To enhance comprehension of the relationship between heat distribution, microstructural evolution, and mechanical properties, a detailed analysis was performed on the microstructural characteristics of Friction Stir Additive Manufactured (FSAMed) Ti6Al4V alloys under various processing parameters. Furthermore, a finite element model was established to accurately simulate both the heat distribution and material flow behavior. The findings indicate that when the central temperature is below β transus temperature (T_β-transus) at a rotation speed of 150 rpm, grain refinement occurs in the stirring zone due to severe plastic deformation and dynamic recrystallization (DRX), resulting in a microstructure consisting of fully equiaxed α and β grains. Conversely, when the rotation speed exceeds the T_β-transus at 300 rpm, the initially refined grains begin to coarsen, and martensite α’ phase along with lamellar (α + β) structures become observable at the center of the stirring zone. Additionally, it was found that slip and twinning serve as the predominant deformation mechanisms during FSAM. Based on the Schmid factor analysis in EBSD data, the pyramidal{10−11} 〈11−20〉 and{10–11} 〈11−23〉 slip systems are identified as being more readily activated. This study establishes a theoretical foundation and provides a valuable reference for future investigations into FSAMed Ti6Al4V alloys.