Optimization Of Heat Treatment Process And Control Of Microstructure And Properties Of 2195 Al-Li Alloy Sheet

As a typical third-generation Al-Li alloy,2195 Al-Li alloy has the advantages of low density,high specific rigidity,good low-temperature mechanical properties and corrosion resistance.It is widely used in the manufacture of lightweight structural parts for space vehicles and so on.Taking 2195 Al-Li alloy sheet as the research object,this paper systematically studied the effects of complete annealing and T8 aging heat treatment on the mechanical properties and microstructure of the alloy sheet,and determined the complete annealing and T8 aging heat treatment system that can achieve the optimal mechanical properties of 2195 Al-Li alloy sheet.providing theoretical support and reference for the 2195 Al-Li alloy is completely annealed and optimizing industrial processes T8 aging sheet.The main research content and research results are as follows:We studied the influence of different annealing process parameters on the microstructure and mechanical properties of 2195 alloy.Recrystallization occurs during the complete annealing of the alloy,and the degree of recrystallization increases with the increase of the annealing temperature,while the annealing holding time and annealing cooling rate have little effect on the degree of recrystallization.After being fully annealed,the texture strength of the alloy is significantly lower than that of the hot-rolled state.As the annealing temperature increases,the dislocation density in the deformed structure of the alloy decreases,the substructures such as small-angle grain boundaries decrease,the proportion of recrystallization increases and grain growth occurs,and the soluble Cu-rich phase continues to dissolve into the alloy matrix.And in the slow cooling process after the annealing treatment,the θ’ and T1 phase are significantly precipitated,which causes the strength performance of the 2195 Al-Li alloy sheet to decrease first and then increase,reaching the minimum value at the annealing temperature of 400℃,and at the same time gaining higher plasticity.The optimal complete annealing process parameters for 2195 Al-Li alloy sheet are determined:annealing temperature is 400℃,annealing holding time is longer than 60 min,cooling rate is 20℃/h-40℃/h,and the furnace temperature is lower than 150℃.Under these conditions,the alloy has the best mechanical properties:tensile strength of 217 MPa,yield strength of 112 MPa,and elongation of 18.0%.We studied the influence of different process parameters T8 heat treatment on microstructure and mechanical properties of alloys.The alloy sheet was subjected to solution treatment at different temperatures and times,and it was found that when the solution temperature was 505℃ and the solution time was 90 minutes,the soluble second phase in the alloy was fully re-dissolved;as the solution time increased,the average the grain size shows a growing trend.Increasing the pre-tensioning deformation can promote the precipitation of the strengthening phase T1 phase.When the pre-tensioning deformation reaches 3%,a large number of fine T1 phases are precipitated in the alloy.Aging time growth will lead to a strengthening phase T1 coarsening,reduce the strengthening effect.As the amount of pre-deformation increases and the aging time increases,the fracture mode of tensile specimens tends to increase in the proportion of brittle fracture.The optimal T8 heat treatment process parameters for 2195 alloy sheet are determined:solution temperature is 505℃,solution time is 90 min,pre-stretching deformation is 3%,aging temperature is 155℃,aging time is 32 h,alloy plate can obtain the best Strength and toughness matching:tensile strength 598 MPa,yield strength 569 MPa,elongation rate 1 1.8%,fracture toughness KIC value 33.1 MPa·m1/2.