Multiphase CFD simulation and experimental investigation of friction stir welded high strength shipbuilding steel and aluminum alloy

This study executed the volume of fluid (VOF) based multiphase computational fluid dynamics (CFD) simulation by incorporating a modified analytical model for dissimilar friction stir welding of DH36 shipbuilding steel and 6061-T6 aluminum alloy. The impact of rotational speed on the temperature and plasticized material flow associated with the tool–material interaction was investigated. The simulation results revealed that the variation in rotational speed was significantly affected the temperature and material flow around the FSW tool. The maximum velocity and strain rate were obtained at the outer edge of the shoulder due to the lowest dynamic viscosity on the Al6061 side. The velocity vectors revealed that the material flow pattern was discontinuous in the advancing side at low heat input, whereas it was improved and became uniform at higher heat input conditions. Transmission electron microscopy (TEM) analysis revealed the formation of a dual-phased intermetallic compound (IMC) layer of FeAl 3 and Fe 2 Al 5 at the interface. Its thickness increased with an increase in rotational speed due to the enhanced intermetallic reaction at a higher temperature and strain rate. The rotational speed of 875 rpm produced the maximum joint strength~207.4 MPa at the IMC layer thickness of 4.83 ± 0.65 µm. The grain structure was refined under dynamic recrystallization, and the hardness improved significantly as the heat generation and strain rate increased. The intercalated structures acted as the hardest zone because of extensive IMCs formation, i.e., Fe 3 Al at 450 rpm and 600 rpm, and Fe 3 Al + FeAl at 875 rpm and 1200 rpm.