Experiment Analysis And Numerical Modeling Of Thermo-mechanical Behavior In Aluminum Squeeze Casting

Squeeze casting is an advanced and near net-shape casting process, in which externalapplied high pressure is used to solidifying castings. The process combines advantages ofcasting and forging methods. The castings are characterized with fine grains and goodmechanical properties. During the casting process, very complex behavior including heattransfer and phase transformation, squeeze pressure transmission, stress and strain, areinvolved. The study on temperature and stress evolution during the solification and modelingof thermal-mechanical fields can enrich knowledgs of the process and provide importantinformation for practical process optimization.A series of experiments were designed to measure the temperatures and pressures incavity as well as die temperatures of ZL101A direct squeeze castings under different appliedsolidification pressures. The evolution and relationship of the measured temperature andpressure were analyzed and discussed. At the beginning of the solidification, the solidifiedshell with thin thickness had larger deformation, improving the interfacial contact of die andcasting and increasing the interfical friction. Therefore, the pressure at casting bottomdecreasd after reaching the peak values. During the later period of solidification, the shell hadlarger thickess and can prevent the deformation so that under50and75MPa appliedpressures, the pressure at the bottom increased wheras the under100MPa applied pressure,the pressure continued to decrease due the applied pressure could forced the shell to deform.It is shown that the applied pressure100MPa can induce more sufficient shrinkage feedingthan50,75MPa. The study indicated that proper dwelling times can be in favior of thefeeding and die life. A coupled thermo-mechanical finite element mathematical model hasbeen developed to simulate the temperature and stress field during squeeze casting process. Inthe temperature model, the enthalpy method was applied to deal with the latent heat and athree level time-stepping method was adopted for solving transient heat transfer problem. Athermo-elasto-visco plastic constitutive model and an ideal elastic-plastic constitutive modelwere utilized to describe the mechanical behavior of the liquid and solidified metal respectively during solidification. The volume contraction and inelastic deformation were alsotaken in account in the stress model. The key factors about the coupled simulation wereproposed and dealed with, such as interfacial heat transfer model, and treatment casting anddie interfical contact, and so on.Base on the established model and finite element method, a C++calculation programwas designed and developed. It has been applied to the experimental castings, and thesimulation results were analyzed. It was shown that as the applied solification pressureincreased the contact at casting and die interfaces were improved, and the calculated castinghad low temperatures with high cooling rates, and the die temperatures were enhanced. Thesimulated stress in the solified shell had high values while the low stressed were found in theinternal liquid regions. With the increased applied pressures, the shell had larger deformationand the region with low stress were smaller. The above results show the reasonability ofestablished model. In the simulation, the evolution of calculated temperatures and pressuresare agreed with the experiment ones which validates the established model.