A Multi Scale Strategy for Simulation of Microstructural Evolutions in Friction Stir Welding of Duplex Titanium Alloy

Abstract

A fully coupled thermo-mechanical model is established to simulate the temperature variations and the material deformations in friction stir welding (FSW) of Ti-6Al-4V. The extracted data are used for further simulation on microstructural evolutions. A multi scale model, which consists of the grain growth model in grain cluster scale and the phase transformation model in one grain scale, is proposed. The nuclei of α and β phases, the recrystallizations and the grain growths are systematically investigated. Comparisons with experimental data and experimental observations can validate the newly proposed microstructural evolution model for Ti-6Al-4V. Results indicate that the volume fractions of α and β phases can be directly determined by the cooling rates in FSW process. With the increase of the rotating speed, the volume fraction of α phase is increased and β phase decreased due to the increase of welding temperature. With the decrease of the translational speed, the volume fraction of α phase gets bigger and β phase smaller. The acicular α grain can be generated on the β grain boundaries and grows along <1 1 0> direction on β substrate. The average length of α grain can be increased with longer cooling time and decreased with lower rotating speed or higher translational speed.