Study On Hot Deformation Behavior And Extrusion Forming Process Of 2195 Aluminum-lithium Allo

2195 Al-Li alloy has the characteristics of low density,high modulus of elasticity,high specific strength and high specific stiffness,and has strong fatigue resistance in the atmosphere and space environment,so it is widely used in aircraft and various spacecraft.However,there have been few studies conducted on the hot deformation behavior and profile extrusion of 2195 Al-Li alloy.Especially,a complete production system has not been formed in the numerical simulation and actual processing of profile extrusion,which limits its further application in the aerospace field.In this paper,the homogenization treatment of 2195 Al-Li alloy is carried out,the thermal deformation behavior is studied,the constitutive equation and hot processing map were constructed.The microstructure and properties of the profile were discussed based on both numerical simulation and actual extrusion processing results.The following conclusions are obtained:（1）In view of the serious defects such as dendrite segregation of cast 2195 aluminum-lithium alloy,the single-stage homogenization treatment of process parameters 400-480°C/16 h and the double-stage homogenization treatment of process parameters 440°C/16 h+470-490°C/20 h were carried out,and the grain structure,phase composition and mechanical properties of the alloy under different process parameters were compared and analyzed.The results show that if the heating temperature is too low during the homogenization treatment,the second phase resolubilization is incomplete,while the excessive heating of the alloy will be caused by too high temperature.The homogenization effect is effective when the heating temperature of the single-stage homogenization treatment is 440°C and the heating temperature of the second stage of the double-stage homogenization treatment is 480°C.When the homogenization system is 440°C/16 h+490°C/20 h,the yield strength and tensile strength of the alloy are 222.6 MPa and 341.5 MPa,the elongation is 14.3%,and the hardness is 127 HV,which is significantly higher than that of the cast alloy.Therefore,the most suitable process parameters for homogenization of cast 2195 aluminum-lithium alloy are 440°C/16 h+480°C/20 h.（2）The hot deformation experiment of 2195 Al-Li alloy was conducted using a Gleeble-3500 thermal simulation testing machine.The experimental temperature ranged from 360 to 510°C and the strain rate varied from 0.01 s^-1 to 10 s^-1.The hot deformation mechanism of the alloy was expounded by studying the true stress-true strain curve,constitutive model and hot processing map.The results showed that the flow stress of 2195 Al-Li alloy decreased with the increasing temperature and increased with the increasing strain rate.In this study,the constitutive equation of 2195 Al-Li alloy was established.The activation energy Q=203.64388 KJ/mol,the structural factor A=1.94387×1014,the stress factorα=0.012951417,and the strain hardening index n=5.88388 were calculated.The Pearson correlation coefficient=0.95684 and the average relative error AARE=9.8079%are calculated by the predicted stress value and the actual stress value,which proves that the constitutive model has high feasibility.The instability range of 2195 Al-Li alloy was determined to be:379-420°C/0.75-10 s^-1 and the safe processing range was found to be 440-510°C/0.01-0.25 s^-1 through the construction of a hot working map.In this region,the alloy mainly underwent dynamic recrystallization.（3）With an"L"shaped solid profile as the research object,2195 Al-Li alloy was used for numerical simulation experiments of extrusion,and 10 extrusion experimental schemes were designed according to different billet preheating temperature,mold preheating temperature and extrusion speed,and the influence of different process parameters on temperature difference（ΔT）,standard deviation of flow rate（SDV）and extrusion force was analyzed.It was found that the extrusion force gradually decreased with the increase of billet preheating temperature and mold preheating temperature,and gradually increased with the acceleration of extrusion speed.The temperature difference and SDV decrease as the mold preheating temperature increases,and increases with the acceleration of extrusion speed.To ensure that the maximum temperature of the profile does not exceed the safe processing range of 2195 Al-Li alloy,the preheating temperature of the blank is 500°C,the mold preheating temperature is 480°C,and the extrusion speed is 0.5 mm/s.（4）The extrusion experiment of 2195 Al-Li alloy after two-stage homogenization treatment was carried out,and the experimental process parameters were determined by combining the numerical simulation results.The extruded profile was subjected to 510°C/90 min solution treatment and 170°C/32 h artificial aging treatment.The macroscopic morphology,microstructure and mechanical properties of the profile were observed and discussed.The results showed that the forming quality of the extruded profile is good,and the mechanical properties are significantly improved compared with the as-cast alloy.During artificial aging treatment,the hardness of the profile is 178 HV,the yield strength is 620 MPa,and the tensile strength is 634 MPa.After artificial aging treatment,δ’（Al₃Li）phase and T₁（Al₂Cu Li）phase can be precipitated and recrystallized.The success of the extrusion experiment showed that the optimal extrusion process parameters obtained by numerical simulation have high reliability,and the numerical simulation technology can be used to guide the extrusion production of 2195 Al-Li alloy profiles.