Numerical Simulation And Optimization Of Aluminum Alloy Die Casting Based On Inlay Casting Process

Bimetallic materials usually have some advantages that single materials don't have,and thus their applications are growing.Not only does die casting process can produce large,complex,thin-walled parts,but also it is easy to implement inlay casting.On the one hand,it's easy to achieve the connection of two different materials by using inlay casting.And inlay casting can not only solve the problems of poor processability,but also can make the compound castings with excellent performances of two or more materials.On the other hand,the workload of assembly can be reduced and the manufacturing process can be simplified by using inlay casting.However,the current researches on solid-liquid bimetallic materials are mainly to analyze the transition layer thickness and organizational structure of the inlaid region through the engineering experiments,which causes some problems,such as a long product development cycle,high production cost.Therefore,in order to optimize the parameters,improve the overall quality of the inlay casting and realize the prediction of the inlaid combination and thickness of transition layer in the structure or process design stage of the product,a magnesium alloy-aluminum alloy bimetallic piston,called magnesium-aluminum dual-alloy piston for short,is studied in this paper.Firstly,this paper describes the relevant theories of the numerical simulation of die-casting filling and solidification process.And based on the theory of heat transfer,the thermal conductivity between the magnesium alloy insert and the aluminum alloy piston matrix is analyzed.At the same time,the diffusion of metal atoms in the case of infinite and semi-infinite diffusion couple is analyzed by using Fick's second law,and the function error solution of Fick's Second Law is obtained.This work provides a theoretical basis for the calculation of diffusion distance of metal atoms in magnesium-aluminum dual-alloy piston.Secondly,the structure of the magnesium-aluminum dual-alloy piston is modeled,the relevant parameters of the numerical simulation are determined and the die casting simulation of the piston is carried out.According to the simulation results,the temperature fields of the aluminum alloy piston matrix and the magnesium alloy insert during the die casting process are analyzed.Based on the bonding mechanism of solid-liquid bimetallic interface and the common defects of die castings,the diffusion time of metal atoms and pore volume are proposed to evaluate the quality of the interface bonding of magnesium-aluminum dual-alloy and aluminum alloy piston matrix respectively.Furthermore,the effects of the four main process parameters:pouring temperature,casting speed,mold preheating temperature and insert preheating temperature on the diffusion time of metal atoms in the interface are investigated by simulation experiments.Virtual experiments are designed using response surface methodology,and regression equations of pore volume and metal atomic diffusion time on the four process parameters are fitted,respectively.Then the fitting accuracy of the model and the influence of the process parameters on the two evaluation indexes are analyzed.In order to improve the quality of aluminum alloy piston matrix and the interface bonding of magnesium-aluminum dual-alloy,diffusion time of metal atoms and pore volume are optimized by multi-objective optimization algorithm:NSGA-II.And better combinations of process parameters are obtained.Finally,based on the optimized magnesium-aluminum dual-alloy piston,the diffusion distance of the main elements in the interface of magnesium-aluminum dual-alloy piston is calculated by using Fick's Second Law.And the prediction of the thickness of transition layer in the bonding interface is achieved by the diffusion distance.