Multiscale numerical investigation on microstructure characteristics with the effect of flow field under different process conditions

Microstructure characteristics formed in the solidification process of molten pool are closely related to the mechanical performances of welded joints. A macro–micro multiscale model is established to calculate the solidification behavior during the laser welding process. The effectiveness of developed model is verified by the consistency between experimental and simulation results. Based on the established model, the effect of transient flow field on microstructure characteristics is analyzed. Furthermore, the temperature field, transient solidification conditions and microstructure characteristics under different process conditions are discussed in details. The results show that the columnar grain during the laser welding process with considering the transient flow field gradually deviates from the vertical direction and exhibits a slightly curved morphology characteristic compared to that without considering the transient flow field. The number of solute-enriched droplets in residual liquid region is decreased and the uniformity of solute concentration distribution is improved with the laser power increasing. The maximum solute concentration and solute segregation degree in columnar grain growth region are increasing gradually with the increase in welding speed. The proposed model is beneficial for understanding microstructure evolution during the laser welding process and refining weld microstructure to enhance the welding quality.