Study On Numerical Simulation And Experiment Of Asymmetric Backward Extrusion Processes For Mg-Gd-Y-Zn-Mn Magnesium High-Strength Alloy

Magnesium alloys have been widely used due to their low density,high specific strength,good damping and vibration reduction properties,and they have gradually attracted the attention of researchers.As an important forming method of wrought magnesium alloys,extrusion mainly includes forward extrusion and backward extrusion.The backward extrusion has the characteristics of less deformation load,shorter stroke and more uniform deformation.Compared with conventional backward extrusion,asymmetric backward extrusion can make the temperature,stress and strain distribution of the alloy in the deformation process become even,so as to refine the grains,weaken the texture and improve the mechanical properties of the alloy.Therefore,on the basis of conventional backward extrusion,it is of great significance to explore the asymmetric backward extrusion process to improve the microstructure and properties of magnesium alloys.This topic firstly uses DEFORM finite element numerical simulation software to numerically simulate the asymmetric backward extrusion process of Mg-Gd-Y-Zn-Mn high-strength magnesium alloys,and analyzes the effect of the different asymmetric backward extrusion methods(differential temperature backward extrusion,rotary backward extrusion,gradient strain backward extrusion)on the alloy deformation process,the more excellent asymmetric backward extrusion process parameters are obtained,that is,differential temperature backward extrusion: the billet temperature is 510°C,the die temperature is 360°C;rotary backward extrusion: the rotation speed is 1.0rad/s;gradient strain backward extrusion: the protruding angle of the side wall of the die is 90°.Then,the finite element simulation method is also used to study the differential temperature backward extrusion deformation process of Mg-Gd-Y-Zn-Mn high-strength magnesium alloy under different billet temperatures and extrusion speeds,analyze the changing laws of temperature field,strain field,stress field and forming load of the alloy during the deformation process,the more excellent differential temperature backward extrusion process parameters are obtained,that is,the initial temperature of the billet and the die are 480°C and 370°C respectively,and the extrusion speed is 0.5mm/s.This provides theoretical guidance for the subsequent differential temperature backward extrusion experiments of Mg-Gd-Y-Zn-Mn high-strength magnesium alloys.Finally,six sets of parameters of the alloy differential temperature backward extrusion experiment were carried out,and it was found that the surface quality of the other alloys was good except for the VZ02 alloy(the billet temperature was 420°C,and the extrusion speed was 1.5mm/s).Under the same parameters,different parts of the alloy show different microstructures.The layered LPSO phase was precipitated in the alloy during backward extrusion.The EBSD characterization results show that the increase of extrusion temperature and the increase of extrusion speed can improve the recrystallization degree of the alloy and refine the grains at the same time.The IPF map shows that the grain orientation of the alloy is deflected,and the rare earth texture in the alloy can weaken the basal texture.The VZ05 alloy in the peak aging state exhibits the more excellent mechanical properties,and its tensile strength,yield strength and elongation are 505 MPa,403MPa and 3.5%,respectively,which are mainly due to finegrain strengthening,second-phase strengthening(layered LPSO phase and bulk LPSO phase)and age strengthening.