Hot Deformation Behavior And Microstructure Of Spray Forming 2195 Al-li Alloy

Compared with the traditional aluminum lithium alloy,the third generation Al-Li alloy has higher specific strength,higher specific stiffness and better weldability,which has been applied in the field of aerospace and can improve the payload and fuel efficiency of spacecraft and aircraft.Due to the anisotropy and poor plasticity of Al-Li alloy,proper hot working process is helpful to improve its processability.In this paper,the hot deformation behavior of 2195 Al-Li alloy was studied by extruded and solution spray forming.The strain rate of the two sampless is 0.01s^-1,0.1s^-1,1s^-1,5s^-1,and the deformation temperature is respectively 300-460?and 380-460?.The conclusion is as follows:With the increase of strain rate and the decrease of deformation temperature,the flow stress of the two samples increases gradually,and the solution samples flow stress is more sensitive to the change of deformation temperature and strain rate.The OM,SEM and TEM were used to analyze the hot deformation structure of extruded and solution,the results show that as the temperature increases,the precipitated phases of extrution state change from??and S?phases at low temperature to??,??and T₁ phases at high temperature.the microstructure of extrution state changes from hot extrusion to dynamic recovery to dynamic recrystallization,and the dynamic recrystallization nucleation of extrution state is formed at the coarse second phase and grain boundary.With the increase of temperature,the tiny second phase of solution state precipitated in the crystal changes into the second phase dispersed along the sub grain boundary.The microstructure of solution state gradually develops from dynamic recovery to dynamic recrystallization,and the recrystallization nucleus forms at the boundary of grain boundary,intragranular with the interface between the coarse second phase and the matrix.With the decrease of strain rate,the degree of dynamic recrystallization increases and the discontinuous dynamic recrystallization changes to continuous dynamic recrystallization near 460?of materials in two states.Through linear regression analysis,the activation energy of extruded and solution samples are 155.0490 kJ/mol and 187.93899 kJ/mol respectively,and the constitutive relationship between deformation temperature,strain rate and rheological stress of the two state is constructed.The correlation coefficient RC between predicted stress and measured stress is 0.98829 and 0.98609,and?is respectively4.68 and 5.67.The accuracy of the prediction equation is verified.Based on DMM model,the hot working diagram of spray forming 2195 Al-Li alloy is established.The instability diagram is obtained by K-P and M-R of instability criteria in extrusion state and solution state respectively.Combined with the hot working diagram and microstructure analysis,the best hot working parameters of extrusion state:410-440?/0.01-0.05 s^-1,440-460?/0.01-0.03 s^-1;the best hot working parameters of solution state:390-435?/0.01-0.3 s^-1,435-455?/0.01-2 s^-1.