Study on solidification process of alloy centrifugal casting

During centrifugal casting, due to the density difference between different alloy components, segregation is easy to occur under the action of centrifugal force. Many researchers have studied the segregation phenomenon in the solidification process of centrifugal casting.

Drenchev et al. Established the coupling model of particle motion and heat transfer in centrifugal casting of particle reinforced metal matrix composites, and studied the solidification process of centrifugal casting of particle reinforced metal matrix composites. In their research, the enthalpy equation is the main governing equation, but the flow of liquid metal (that is, the filling process) is not introduced in the solution, so the wall thickness of the casting is always a constant value, and the wall thickness of each place is equal.

Liu et al. Established a theoretical model to predict the gradient distribution of particles in centrifugal casting gradient materials. In the model, the movement and solidification process of particles in liquid metal were solved simultaneously. They also discussed the factors affecting the particle distribution in detail. The results show that there are composite area and blank area in the gradient composite, and the area distribution can be controlled by changing the density difference between particles and liquid metal. In order to verify the theoretical model, experiments were carried out with aluminum matrix composites, and the experimental results were consistent with the theoretical model results.

Wu et al established a multi-scale model to simulate the microstructure change of Ti-6A1-4V alloy during vertical centrifugal casting. The model is the coupling of 3D finite difference method and 2D cellular automata, in which the finite difference method is used to calculate the flow, heat and mass transfer process of liquid metal in centrifugal casting, and the cellular automata is used to predict the nucleation and growth of crystal in microstructure. An improved algorithm based on Cellular Automata for predicting shrinkage defects in castings is also presented. Using the established model, they studied the influence of mold speed, superheat, mold material and other factors on the microstructure, and analyzed and discussed the mechanism. The results show that the range of equiaxed grains increases with the increase of mold speed, but decreases with the increase of superheat and thermal diffusion coefficient, and the influence of rotational speed is more important than that of superheat and other factors The impact is much more significant.

Chang et al. Established a coupled stochastic model to predict the change of grain structure during centrifugal casting solidification. The model consists of two parts: one is cellular automata, which is used to simulate the evolution of microstructure; the other is finite volume model, which is used to calculate the heat transfer process. They used the model to simulate the centrifugal casting process of A1 alloy, and studied the effects of mold speed, alloy concentration, metal superheat and initial preheating temperature on the microstructure of the solidification process. The results show that proper rotation speed, lower superheat, lower preheating temperature and slightly higher alloy concentration are beneficial to the formation of equiaxed grains.

Kang et al. Carried out one-dimensional heat conduction analysis of centrifugal casting process of aluminum alloy and copper matrix metal composites. The particle segregation model was solved by changing the volume fraction of particles, and the heat conduction equation was solved by finite difference method. The results show that: mold speed, solidification time and density difference between matrix phase and reinforcement phase have great influence on the thickness of segregation zone; when matrix phase density is greater than reinforcement phase density, the thickness of particle enrichment zone near inner edge decreases with the increase of mold speed; solidification time is also related to mold speed, and solidification time decreases with the increase of mold speed.

Song et al. Established a program to solve the solidification process and eutectic carbide segregation in horizontal centrifugal casting. According to the geometry of work roll, the coordinate system is cylindrical coordinate system, and the initial temperature field of solidification process is obtained according to the temperature field at the end of filling process. The results show that: the temperature field is “sandwich” shape, the cooling rate of the area near the outer wall and inner wall is faster, the temperature is lower, and the temperature in the center is higher; in addition, under the effect of centrifugal force, the segregation of MC particles is very obvious, which is divided into four areas along the radius direction, and the content of MC particles near the mold is very small, which is because of the metal near the mold The liquid soon solidified. They also made experiments to verify the theoretical results, and the experimental results are in good agreement with the theoretical calculation results.