Simulation For Dendritic Growth Of Aluminum Alloys With Melt Convection Based On The LB-CA Coupled Model

During the research of material process and performance, it not only costs moremanpower and material resources, but also gets unsatisfactory result in some aspectsif chosen conventional experimental methods.It provides a very important means tosolve practical problems in material science with the development of computertechnology.More and more researchers focus on the investigation of themicrostructure formation mechanism of various materials via the computersimulation.In this thesis, numerical simulation has been carried out to investigatemicrostructure characteristics of dendritic growth in the presence of naturalconvection in the melt.It is greatly significant to improve the fundamentalunderstanding of the mechanisms of the microstructure formation during thesolidification process, and to control the process conditions or parameters of thesolidification.In this thesis, melting natural convection model was established in closed squarebased on the theory of lattice Boltzmann.The treatment effect, such as the meltingprocess, latent heat release, outside force, solid-liquid fuzzy interface and outsideboundary, stability and accuracy were verified in this model.Investigating the effecton forced convection to melt natural convection under the additional mandatory speed,and discussing the rationality of the influencing from the additional outside boundaryspeed in the computational domain in the established LB models.The coupling model of Lattice Boltzmann and Cellular Automata was furtherestablished for investigating the growth situation of single dendrite.There mainlyincludes：the rationality of the distribution of temperature field and solubility fieldwas discussed; The growth of the secondary dendrite arm caused by the handling ofsolute segregation was considered and the influence of fluid velocity field caused byextrapolated velocity of acute interface between solid and liquid phase wasinvestigated.The growth model of dendrites in convection was established via couplingprocedure, and the formation mechanism of dendrite morphology was studied.The results show that the growth effect varied in upstream and downstream secondarydendrite arms at different convection velocity.The influence of convection velocity onsecondary-dendrite arm has showed that the growth of upstream secondary-dendritewas more obvious than downstream secondary-dendrite at a greater convectionvelocity.The preferred direction of dendrite growth has been changed by modifyingthe optimal angle in original cellular automaton model.By this method, the influenceof optimal angle on dendrite morphology showed that there was a different growthspeed in upstream and dowmstream dendrite arm because of the difference intemperature and solubility fields along velocity direction.