Numerical Simulation Of Microstructure And Mechanical Property Of Aluminum Alloy During Solidification And Heat Treatment Processes

The development of automotive lightweighting has put forward higher request on the mechanical properties of aluminum alloy casting.The mechanical properties of aluminum alloy casting are determined by the microstructures in different scales,whose formation is influenced by solidification and heat treatment conditions.Using the numerical simulation technology to investigate the evolution of microstructure and mechanical properties during solidification and heat treatment processes has important academic significance in quantitatively understanding the relationship between process,structure and property.Meanwhile,carrying out the modeling and simulation through combining with the actual production,and developing industrial applicable models are of great application value for foundry enterprise to produce the high quality and low cost aluminum alloy castings.Through analyzing the solidification path and microstructure characteristic of Al-7Si-Mg aluminum alloys,and coupling with Pandat software package in combination with thermodynamic/kinetic/equilibrium phase diagram databases,a multicompent and multiphase cellular automaton(CA)model was developed to simulate the growth of dendrite and irregular eutectic.Based on the cooling curves and microstructure of step casting as well as the reasonable nucleation assumptions,a theoretical equiaxed nucleation model suitable for Al-7Si-Mg alloys under ordinary casting conditions was established.Using these models,the growth of dendrite and irregular eutectic in Al-7Si-Mg alloys was simulated.The influence of undercooling,alloying composition,interaction between solutes,cooling rate and solid diffusion etc on the dendrite growth,and the evolution of Al-Si irregular eutectic microstructure in unmodified or Sr-modified conditions were analyzed.Meanwhile,corresponding experiments were carried out to validate the simulated dendrite and eutectic morphology as well as the microstrcuture characteristic parameters,and well agreements were found between experimental and simulated results.Using the step casting and sand casting test bars,the relationship between process,structure and property in Al-7Si-Mg alloys was systematically studied,and the influence of as-cast microstructure refinement,alloy composition and heat treatment parameters on the microstructure and mechanical properties was analyzed.Based on the analysis of experimental data,a yield strength model for Al-7Si-Mg alloys was established,and the relationship between yield strength and ultimate tensile strength was obtained by data fitting.Precipitation kinetics model,strength model and strain hardening model were established,and the microstructure simulation and tensile property prediction during heat treatment process were carried out.The simulated results were vadilated by experimental results.The influence of solution temperature,aging temperature and alloying composition on yield strength,and the influence of aging treatment and as-cast microstructure refinement on the stress-strain curve during tensile process were quantitatively analyzed using these models.Finally,the limitations of present models and the factors influencing the prediction precision of tensile properties were discussed.Through process and multiscale simulations for several aluminlum castings were carried out which involvs the macroscopic temperature field calculation,ascast microstructure simulation and the final tensile property prediction.The predicted results were consistent with the experimental results.It demonstrated that this numerical approach can well correlate the relationship between process,structure and property,and can provide the optimized process parameters for aluminum casting production.