Numerical Simulation Of Multiphase Flow During Mold Filling Of Particle Reinforced Composites

Particle-reinforced metal matrix composites(PMMCs) are widely used in the fields of modern aerospace, transportation, electronic packaging field because of their high specific modulus, high specific strength, isotropy and so on. Among the preparation methods of PMMCs, casting process is one of the most popular methods due to its advantages including low cost, high production efficiency, and capability of forming components in complex shapes. During casting process, the composite flow behavior has important effects on particle distribution, and determines the casting performance. For the purpose of understanding characteristic of mold filling of PMMCs to improve foundry technology and the homogenization of particle distribution and then promote development and application of PMMCs, in this thesis, the slurry flow and particle distribution during mold filling process of PMMCs were investingated by numerical simulation and experiment.Based on the theories of foundry and multi-phase flow dynamics, the Eulerian-Lagrangian method was used for establishing the mathematical model of multi-phase flow during mold filling process of PMMCs. The liquid metal was regarded as continuous phase, whose continuity, momentum and energy equations were established by the Euler method. The reinforcing particles were treated as discrete phase, and its motion equations were calculated by the Lagrangian coordinate. The direct finite difference method(DFDM) was used to discretize the mathematical model, and its velocity field and pressure field were solved through the SOLA iteration method.The particle collision during mold filling process was investigated, and a particle collision model which combines with hard sphere model and soft sphere model was established. At first, the probability of a particle collide with other particles was determined through the direct simulation Monte Carlo(DSMC) method. Then the modified Nanbu method was used to define the possible collision objects, and the effect of particle collisions on particle movement was described by a collision force. In addition, the pre-processing of initial and boundary conditions during the mold filling was proposed. Pressure or velocity boundary can be used for the fluid, while the velocity boundary for particle inlet condiction was set. For the casting and mold interface, no-slip boundary condition was used. Based on the established mathematical model, the calculating program of every term was designded using C++ language and then a multi-phase program for mold filling process of PMMCs was developed.The experiments of vertically upward suction casting for A356/Si Cp composites with different particle sizes were designed and performed. The Si Cp contents at different regions were quantitatively measured and the Si Cp distribution in the casting was studied. The developed multi-phase program of mold filling process of PMMCs was applied to the upward suction castings of A356/Si Cp composites. The simulation results were compared and validated with the experimental data. The Si Cp distribution in the casting central and near the mold surface was analyzed and investigated.The in-situ observation of mold filling processes of PMMCs with real-time X-ray radiography was first conducted.The flow behaviors during mold filling of the A356/Si Cp investmeng casting were studied, and the Si Cp contents in casting different parts were quantitatively measured and analyzed. With thedeveloped simulation program of multiphase flow, the filling process of A356/Si Cp investment casting was simulated, and the results of simulation and experiment were compared and analyzed. The effects of the flow behavior on particle distribution in PMMCs were discussed.