Coupling phase-field model and CFD for hot cracking predictions of Al-Li alloys

To improve the prediction of hot cracking, fluid flow, and dendritic growth must be investigated quantitatively and thus an integrated 2D model of coupling phase-field model together with CFD calculations was proposed in this work. First, a phase-field model for thermodynamics of binary Al-3.3wt.%Li was developed based on the CALPHAD database. The columnar dendrites with different orientation angles (0°-28°), different grain sizes of equiaxed grains, and columnar to equiaxed transition (CET) were simulated. Then, CFD calculations were performed based on geometries from simulated microstructure features to predict the inter-dendritic pressure distribution. The RDG model and Kou model were used to evaluate the hot cracking susceptibility (HCS) of these simulated microstructure features. Comparing to the RDG model, our simulations have shown that the feeding pressure drop varies as a function of grain orientation, while it is a constant in the RDG model. It is found that equiaxed crystals with large grain sizes have high HCS due to their large pressure drop as well as the narrow liquid channel. The Kou model is considered unable to calculate the HCS of CET because the value of dT/df_s^1/2 near f_s=1 of CET and pure equiaxed crystals are the same. The predicted pressure drop of CET using our integrated model shows that the equiaxed crystals have a great impact on a the liquid feeding of columnar crystals when f_s=0.51.