Modeling of Investment Casting of Ti48Al48Cr2Nb2 (at%) Alloy Air Rudder Skeleton

The air rudder skeleton has an asymmetric complex structure with high casting difficulty, making defects such as shrinkage porosity easy to develop during the casting. Based on the structural analysis, a finite element model of the Ti48Al48Cr2Nb2 (at%), i.e., Ti-33.35Al-2.68Cr4.79Nb (wt%), alloy skeleton has been developed by ProCAST software to study its centrifugal investment casting process. In this work, an orthogonal modeling with 4 factors and 3 levels was designed to investigate the influence of process parameters on shrinkage porosity and thus to develop the casting process that is suitable for air rudder skeleton. The optimization scheme was studied in terms of the filling and solidification processes as well as the casting defects, especially in the formation mechanism of shrinkage porosity. The results show that the shrinkage porosity is mainly located at the intersection of stiffeners and near the junction between the ingate and the casting, as a result of a small heat dissipation area for the above positions, which tends to form isolated liquid-phase zones. The formation of the isolated liquid phase in the frame is closely related to the large number of columnar grains and a few equiaxed grains working together to form a grain frame that hinders melt flow, whereas its formation in the solid region is mainly due to a closed area formed by generous equiaxed grains. Finally, the simulation of stress concentration was implemented for optimization of the shakeout time to avoid cracking, and the result was 1300–2220 s.