Study On The Heat Treatment On Microstructure And Properties Of 2195?2050 Al-Li Alloy

Due to its excellent comprehensive properties,2050,2195 Al-Li alloy is widely used in the field of aerospace abroad.In China,there have been many researches on adding elements to strengthen the properties of 2195 Al-Li alloy,and some researches on the effects of aging process or pre-deformation on the microstructure and properties.However,there are few studies on multivariable controlled thermo-mechanical treatment,and few studies on the thermal stability and low temperature and high temperature mechanical properties of 2195Al-Li alloy.At present,most studies on the 2050 Al-Li alloy are about the properties of raw materials including the homogenization,but few about the effect of thermo-mechanical treatment on the microstructure.Both Al-Li alloys have not been widely used in the domestic aerospace field.In order to get better thermo-mechanical treatment process,the orthogonal experimental optimization method,OM,SEM,TEM,electronic universal testing machine were used to investigate the microstructure and mechanical properties and structure of 2195,2050 Al-Li alloy under different solution temperature,pre-deformation,aging temperature and aging time.The mechanical properties of 2195,2050 Al-Li alloy at low temperature and high temperature,the mechanical properties and corrosion properties of the materials after thermal stabilization were studied systematically.Through the study of the T6,T8 heat treatment process of 2195,2050 Al-Li alloy,we found that:In the T6 heat treatment process,the sequence of the three process parameters is aging temperature>aging time>solution temperature in the yield strength,tensile strength and ductility factors in the mechanical properties of the 2195,2050 Al-Li alloy.In the T8 heat treatment process,for the yield strength,tensile strength and ductility performance indexes of two Al-Li alloys,the aging stability is the most important factor,and the solution temperature is the least influential factor.The effect of aging time on the strength of 2195 Al-Li alloy is slightly higher than that of predeformation.The effect of aging time on the strength of 2050Al-Li alloy is slightly lower than that of predeformation.After T6,T8 heat treatment,the main precipitated strengthening phases of 2195,2050 Al-Li alloy are T₁ phase,?'phase and?'phase,with T₁ phase as the main one.The amount of T₁ phase precipitated from 2195 Al-Li alloy was more than that of 2050 Al-Li alloy,and the amount of?'phase precipitated from 2195Al-Li alloy was less than that of 2050 Al-Li alloy.Compared with?'phase,T₁ phase has better strengthening effect on materials.Therefore,compared with 2050 Al-Li alloy,2195 Al-Li alloy has better strength performance.In the continuous aging process,T₁ phase is continuously precipitated and grown up and dissolved with the consumption of?'phase and?'phase.The strength of the material increases with the continuous improvement of aging,reaching the maximum strength at the peat of aging.After that,material entered the overaging stage,and the strength of the material declined.Through the study of the low temperature mechanical properties of materials under different predeformation parameters,we found that 2195,2050 Al-Li alloy have excellent low temperature mechanical property.Test temperature from room temperature dropped to 0?,and then to-70?,the lowest to-196?,the yield strength and tensile strength are significantly improved.For the two Al-Li alloys,the material strength at 7%predeformation is slightly higher than that at 3%predeformation,but the strength difference is less than 5%,and the strength difference does not increase with the decrease of temperature.The optimum heat treatment parameters of the two Al-Li alloys were obtained.The heat treatment scheme of 2195 Al-Li:solution temperature is 510?,pre-deformation is 3%,aging temperature is160?,and aging time is 18h.The heat treatment scheme of 2050 Al-Li:solution temperature is 525?,pre-deformation is 3%,aging temperature is 160?,and aging time is 18h.Under the optimal heat treatment scheme,the two Al-Li alloys can maintain a certain mechanical strength at 100?and 200?.The thermal stability of materials under optimized process was studied.We found that the intergranular corrosion resistance of 2195 Al-Li alloy and 2050 Al-Li alloy were similar and both of them were excellent.In the thermal stability of test temperature is 100?and 120?,of time is 10h,2195 Al-Li alloy remained the intergranular corrosion resistance close to 2050Al-Li alloy,but with the increase of the thermal stability of temperature and the extension of time,intergranular corrosion resistance of 2195 Al-Li alloy decreased obviously,2050 Al-Li alloy still retained the ability to a high intergranular corrosion resistance.2050 Al-Li alloy showed better corrosion resistance than 2195 Al-Li alloy in the exfoliation corrosion test.With the increase of the thermal stability of temperature and the extension of time,the peeling corrosion sensitivity of the two Al-Li alloys increased gradually.2195 Al-Li alloy showed the corrosion grade above EB earlier.Through the study of the effect of the thermal stability on mechanical properties of materials,we found that the strength of the two Al-Li alloys under the optimum heat treatment process changed little when the temperature of thermal stability is not higher than 150?,and the strength still keep close to the peak aging intensity.The strength of the two Al-Li alloys were markedly reduced under the thermal stability test of270? and 10h.