Research On Homogenization Treatment And Hot Deformation Of 2195 Al-Li Alloy Ingot

The outperformance of low density,high elastic modulus and high specific strength promotes 2195 Al-Li alloy broadly applied in the launch vehicle fuel tank.In this paper,the as-cast 2195 Al-Li alloy was studied systematically and diligently on the effects of homogenization treatment and hot deformation parameters on the microstructure via a variety of analysis and testing methods including hot compression test,optical microscopy（OM）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,and electron backscattered diffraction（EBSD）,which served as a reference for the industrial manufacturing.The main conclusions are as follows:（1）The dendritic structure in the alloy ingot can be effectively eliminated by double-step homogenization treatment.The optimized homogenization treatment parameters were determined as 460°C/16 h+515°C/20 h.The coarse eutectic phases at the grain boundary and intragranular precipitates are basically dissolved,and the element segregation could be significantly reduced after double-step homogenization treatment.The experimental results were congruent with the dissolution-diffusion kinetics analysis conclusions.（2）Compared with the single-step homogenization treatment（515°C/20 h）,the higher Zr solute supersaturation after double-step homogenization treatment provides sufficient nucleation driving force,which enables the precipitation of finer,denser and uniformly distributed Al₃Zr dispersoids within and near the grain boundary.Al₃Zr dispersoids exhibit linear and block-like clusters simultaneously and uniquely due to the dislocation morphology and local Zr solute concentration.（3）The effective impediment of recrystallization behavior during solution treatment after plastic deformation is attributed to the fine and dense Al₃Zr dispersoids providing a great Zener pinning effect.The limitation of grain growth,the reduction of recrystallization degree,and the increase of the proportion of low-angle interface provide ideal nucleation sites for the precipitation of the subsequent aging strengthening phases,in marked contrast to the single-step homogenization treatment.（4）The calculated hot deformation activation energy of the alloy is264.303k J/mol based on the true stress-strain data after the correction of friction-temperature difference obtained from the hot compression test.Then,the phenomenological constitutive model and recrystallization kinetics model of the alloy during hot deformation were both established to predict the flow stress and recrystallization softening fraction during the whole hot deformation process,respectively.The error analysis results confirmed that the two models are capable to predict accurately.（5）The primary dynamic softening mechanism of the alloy is dynamic recovery when processed at low deformation temperature and high strain rate（high Z values）.However,the T₁and cubic precipitates significantly hinder the dynamic recovery process via a strong Zener pinning effect,at the deformation temperatures range of 300-400°C,thereby providing large energy storage and promoting the occurrence of discontinuous dynamic recrystallization behavior.With the decrease of strain rate and the increase of deformation temperature（low Z values）,dislocations obtain stronger mobility,resulting in the dynamic recrystallization mechanism gradually transforming into continuous dynamic recrystallization.