Study On The Deformation Behavior And Hot Extrusion Forming Technology Of As-Extruded Mg-Gd-Y-Zn-Mn Alloy

Magnesium(Mg)and magnesium alloys have the advantages of high specific strength,good damping and shock absorption,and easy recycling as it is the lightest metal structural materials.They own broad application prospects in the fields such as automobiles,electronic communications and aerospace.However,there is imited slip system leading poor plastic deformation ability under the room temperature,since the magnesium alloy has a close-packed hexagonal struture.The doping of rare-earth(RE)elements,such as Nd,Gd,Y and Ce,into the Mg alloy can significantly enhance its formability associated with the material strength.The high-strength magnesium alloy material in the Mg-RE-Zn series have excellent mechanical properties and shows relatively good application prospects.Currently,the researches on the extrusion or the rolling process of high-strength magnesium alloys have been increasingly mature,but the research on the secondary deformation of high-strength magnesium alloys is still deficient.This thesis studies the extruded Mg-9Gd-4Y-lZn-0.8Mn alloy and conducts the hot compression experiment with the Thermecmastor-Z thermal simulator.Herein,the constitutive equation and the processing maps were established and depicted,while the optimal processing interval of the extruded Mg-9Gd-4Y-lZn-0.8Mn alloy was obtained as well.Based upon the constitutive equation constructed form the hot compression data,the finite element analysis software Deform-3D was applied to simulate the extrusion of the extruded Mg-9Gd-4Y-lZn-0.8Mn alloy.The effects of different deformation temperatures and different extrusion rates on the equivalent stress,equivalent strain,temperature field and extrusion force were also analyzed and compared in this study.The main conclusions are drawn as follows:? Extruded Mg-9Gd-4Y-lZn-0.8Mn alloy was tested to hot compression experiments with Thermecmastor-Z thermal simulator.The thermal deformation condition has a great influence on the flow stress of the extruded Mg-9Gd-4Y-lZn-0.8Mn alloy.The flow stress increases with the decrease of the deformation temperature and the increase of the strain rate.The activation energy and stress index of the extruded Mg-Gd-Y-Zn-Mn alloy were 188.207 KJ/mol and 2.25385,respectively.The constitutive equation of the extruded Mg-Gd-Y-Zn-Mn alloy is:?=1.5519×10¹³[sinh(0.0154769?)]^2.25385exp(-188207/RT).?The processing maps of the extruded Mg-9Gd-4Y-lZn-0.8Mn alloy were depicted.Most of the rheological instability occurred in the high strain rate region.With the region,most of the energy absorbed by the alloy was used for the structural evolution.Therefore,the minimum power dissipation region was also contained in the high strain rate region.The optimal processing interval of the extruded Mg-9Gd-4Y-lZn-0.8Mn alloy falls between the 420? and the 500? with a strain rate starting from 0.1 s^-1 throughout 1s^-1.?The extrusion process of the extruded Mg-9Gd-4Y-lZn-0.8Mn alloy was numerically simulated by the Deform-3D.The extrusion force experienced three processes of slow increase,rapid increase,and moderate decrease in up and down fluctuations during the deformation process.Additionally,the equivalent stress,equivalent strain,and temperature changed were all concentrated in the extrusion die(the main deformed part of the billet).Under certain conditions,the higher the extrusion temperature is,the lower the equivalent stress is.Similarly,with more uniform more temperature distribution and less extrusion force,the equivalent stress is larger when the extrusion rate getting faster.The temperatures is higher as well as the temperature difference between the billets,once the equivalent strain distribution is much uniform and the equivalent strain value is smaller.