Study On Hot Deformation Behavior And Microstructure Evolution Of 2397 Al-Li Alloy

In aerospace industry,the application of new lightweight structural materials has been a hot topic for years due to the demand of lightweight.One of the most popular lightweight structural materials is Al-Li alloys because of its low density,high elastic modulus,high specific strength,high specific stiffness,low fatigue crack growth rate and good low temperature performance.The main method of forming Al-Li alloy components is plastic forming and the proformance of components is greatly affected by forming process.Therefore,the hot deformation behavior and microstructure evolution mechanism of Al-Li alloy during plastic forming were systematically studied in this paper.2397 Al-Li alloy,a third generation Al-Li alloy,was chosen as the research mateial.The effects of deformation parameters on hot deformation behavior and microstructure evolution were studied by hot compression test and electron backscatter diffraction?EBSD?technology.Moreover,based on the EBSD,a geometrically necessary dislocation measurement program was developed to analyze the coordinated deformation behavior between grains with different orientations.It shows the coordinated deformation capacity has an obvious impact on microstructure evolution.The main results are as following:By hot compression tests,the hot deformation behavior of 2397 Al-Li alloy was studied.The flow curves show steady-state rheological characteristics and dynamic softening tendency during unidirectional isothermal compression.The constitutive equation of 2397 Al-Li alloy was established.It shows the deformation temperature and strain rate have little effect on the deformation activation energy of 2397 Al-Li alloy.However,the effect of strain on the activation energy is obvious.As the strain increases,the deformation activation energy of 2397 Al-Li alloy increases from 208.7KJ / mol to 255.7KJ / mol.This increase of deformation activation energy is due to the fact that,as strain increase,the transformation from low angle boundaries to high angle boundaries is also participated in dynamic recrystallization besides the grain boundary migration.By EBSD,the dynamic recrystallization of 2397 Al-Li alloy during deformation was analyzed.The dynamic recrystallization process of 2397 Al-Li alloy is not sensitive to temperature,but it is greatly affected by the strain rate.At high strain rates(???= 0.1s^-1),LABs are abundantly formed,but do not have enough time to transform into HABs,resulting in insufficient dynamic recrystallization.At low strain rates(???= 0.001s^-1),LABs has enough time to transform into HABs,resulting in a high degree of dynamic recrystallization.A dynamic recrystallization model of 2397 Al-Li alloy was established based on interface evolution.It is indicated that the formation of dynamic recrystallization grains are controlled by grain boundary bulging at early stage of deformation.As deformation increases,the formation of dynamic recrystallizations is controlled by the grain boundary buiging and the transformation from LABs to HABs.By EBSD and geometrically necessary dislocation measurement program,the coordinated deformation behavior between grains with different orientations in 2397 Al-Li alloy was analyzed.In sample mainly contains combination of <001> and <111> orientated components,<111> orientation grains have small Schmid factor and would occur large orientation rotation during deformation.The orientation rotation of <111> orientation grains would force orientation rotation to occur in adjacent <001> orientation grains,since the deformation coordination capacity of <001> and <111> orientation combination is poor.In sample mainly contains combination of <001> and <101> orientated components,both <001> and <101> orientation grains have large Schmid factors,so there is no need for obvious orientation rotation to occur.Moreover,the deformation coordination of <001> and <101> orientation combination is strong,so the deforamtion grains would not be obviously affected by the adjacent grains to occur orientation rotation.In order to evaluate the deformation coordination between the grains,the deformation coordination factor ??is proposed.The smaller the deformation coordination factor,the weaker the deformation coordination between the grains.After statistical caculation,the average deformation coordination factor between the <001> and <111> orientation groups was 0.53,which is less than the average deformation coordination factor of 0.67 between the <001> and <101> orientation groups.Then,the subgrain size prediction model considering the combination of orientations was established.It shows the subgrain size was smaller in the material with weaker deformation coordination.