Numerical Simulation Of Microstructure Evolution Of Al-Si Alloy During Solidification

Al-Si alloys have get the rapid development in the automotive and aerospace industries due to its unique comprehensive properties.However,the difference of the casting process makes the properties of the alloy vary greatly.Different solidification methods will produce different microstructures,which will result in differences in macroscopic properties between the same component or different component alloys.In order to accurately control the macroscopic properties of the alloy,it is necessary to understand the evolution of the microstructure so as to develop a reasonable casting scheme.But the solidification structure is affected by a combination of some external factors(cooling rate,composition,etc).It is difficult to explore the effect of individual factor on the microstructure of the alloy under experimental conditions.As an effective supplement of experiment,numerical simulation technology has a few limitations and can reproduce the evolution of microstructure of the alloy,thereby greatly shortening the experimental period.Based on the theory of cellular automaton(CA)model,the nucleation growth models of aluminum-silicon eutectic,primary aluminum dendrite and primary silicon are established on the Visual Studio 2010 MFC platform using C++ language.First,according to the growth characteristics of aluminum-silicon eutectic microstructure,the paper adopts an alternative nucleation mechanism.The variation of critical nucleation concentration of alternative nucleation model under different undercooling is determined by comparing the experimental results and the simulation results.Based of this,a solidification model of eutectic Al-Si alloy is obtained.For the primary aluminum,a growth model of primary aluminum is obtained by introducing an anisotropy function and a decentered square algorithm.For primary silicon,a two-dimensional planar primary silicon growth model corresponding to octahedral primary silicon is established by analyzing the growth method of octahedral primary silicon and introducing an interface capture rule suitable for the growth of primary silicon in two-dimensional space.The solidification process of Al-13Si(near eutectic)is simulated using the eutectic Al-Si alloy solidification model.And reproduce the evolution of Al-Si eutectic microstructure.Then,the hypoeutectic Al-Si alloy solidification model is established by coupling the primary aluminum dendrite growth model and the eutectic Al-Si alloy solidification model.And the primary aluminum dendrite and eutectic microstructure of Al-1OSi are simulated using the coupled model.Similarly,the solidification model of hypereutectic Al-Si alloy is obtained by coupling the primary silicon growth model and the eutectic Al-Si alloy solidification model.Then the solidification process of Al-15Si and Al-20Si are simulated using this model to reproduce the evolution of primary silicon and eutectic microstructure.In addition,The effect of cooling rate on the solidification structure of Al-10Si,Al-13Si and Al-20Si are studied by casting wedge specimen.By designing a cylindrical mold and selecting Al-15Si and Al-20Si as research alloys,the effect of silicon content on the morphology of primary silicon is explored.The accuracy of above models are verified by comparing the microstructure of the experiment and the simulation results.