The Polycrystal Plasticity Based Thermo-mechanical-dynamic Recrystallization Coupled Modeling And The Integrated Computation On Magnesium Extrusion Process

As the lightest structure metal material,magnesium and its alloys have been widely used in the fields of aerospace,automobile,electrical instruments,etc.The hot extrusion process will improve the formability of the magnesium alloys as the extruded alloys will show more uniform microstructure and higher forming precision compared to as-cast alloys.The dynamic recrystallization(DRX)behavior will always occur during the hot extrusion process,which will greatly refine the grain size of the material.Moreover,the thermo-mechanical effect and variation of strain path of material will have obvious influence on the deformation on mechanical behavior,microstructure evolution and texture distribution during the hot deformation process of magnesium alloys.In this article,the experimental observation and the thermo-coupled modeling analysis were taken on the Mg-1Al magnesium alloy to study the hot forming process of the material.Upon the study of the hot forming process,an integrated computation method was founded to study the hot extrusion process of the magnesium alloy in both macro and micro scale.(1)Experimental analysis on the uniaxial compression process of the Mg-1Al magnesium alloy.The hot deformation process including uniaxial compression were taken on the homogenized cast Mg-1Al alloy at elevated temperatures and strain rates.The microstructure and texture evolution of the deformation were observed by XRD and EBSD methods.The mechanical response,microstructure and texture evolution of the material at elevated deformation conditions were obtained by the isothemal tests,and were used for the parmater fitting in the modeling section.The feedback system in the Gleeble machine was used to obtain the isothermal deformation results at high strain rate,and by comparing the thermal-mechanical results,the deformation induced temperature rise was evaluated quantitatively.(2)Thermo-coupled-crystal plasticity-dynamic recrystallization(TMCP-DRX)modeling.The dislocation density based VPSC-DRX model was extended to magnesium alloys with multiple types of slip systems,and was combined with thermo-mechanical coupled computation.The parameters of the model for the homogenized Mg-1Al alloy were obtained from the isothermal compression results.The evolution laws describing the relationship between parameters and deformation conditions were built,so that the model can describe the deformation behavior of the material at any temperature and strain rate in a certain range.The model was then validated first by a temperature changing deformation and applied in studying the thermal-mechanical effect in the high strain rate compression deformation.(3)Experimental analysis on the hot extrusion process of magnesium alloyThe round extrusion process was taken on the Mg-1Al alloy at different ram speeds to study the thermal-mechanical effects in the process,and the variation of strain path of material was also studied by the designed experimental process.After that,the study was taken on the profile extrusion of the Mg-1Al alloy to evaluate the microstructure and texture evolution at different extruded areas in the cross section.(3)Integrated computation of hot extrusion process of magnesium alloyBy combining upper bound theory,flow line modeling and FEM with the TM-VPSC-DRX model,the intergrated computation method was used to simulate the extrusion process of magnesium alloy.The model was used to study the thermal-mechanical and strain path influence on the deformation of round extrusion and profile extrusion process,and the deformation was evaluated quantitatively.