Effect Of Rolling Deformation On Microstructure And Properties Of 2297 Al-Li Alloy

2297 Al-Li alloy has wide and great prospect in the field of aerospace applications because of its many advantages,such as moderate strength,low density,high elastic modulus,good resistance to stress corrosion and high resistance to fatigue crack growth and so on.In order to further explore the related technology and properties of the alloy,two kinds of 2297 Al-Li alloys with different supplied coditions were used in this study.The hardness and strength were tested.The microstructure of the alloys were characterized by optical microscope(OM),X-ray spectrometer,scanning electron microscope(SEM)equipped with energy dispersive,X-ray spectrometer(EDX)and transmission electron microscopy(TEM).The influence of rolling redutions on the T6 treatment condition and its microstructure and properties of 2297 Al-Li alloy was studied.The rolling possibility of 2297 alloy plate in T8 condition was investigated.The main results are as followings:(1)The microstructure of the as-cast 2297 alloy(A)consists of equiaxed α-Al grains,coarse Cu-rich phases at grain boundary and a small amount of Fecontalning phases.There are obvious dendrite segregation phenomena.Segregation of the main alloying element Cu is observed at the grain boundary.The grains of the 2297 alloy in T8 codition are elongated along the rolling direction,with different degrees of recrystallization.And the second phase particles rich in Cu and a small amount of Fe are discontinuously distributed along the rolling deformation direction.The mechanical properties of alloy B plates show anisotropy.The tensile strength,yield strength and elongation of the alloy are 484MPa,442MPa and 13.8%,respectively.(2)The optimum solid solution temperature of the 2297 Al-Li alloy plates is 535℃,which is independent of the rolling redution and the original state of the alloy.When the solid solution temperature increased from 520℃ to 535 ℃,the number of the second phase particles remaining in the matrix was further reduced,the degree of solution was further increased,but the size of grains increased.When the solution temperature increased to 550 ℃,although the solubility of the alloying elements further increased,but the degree of recrystallization of the alloy becomes larger and grains start coarsening,resulting in a decrease in the mechanical properties.(3)With the increase in rolling deformation,the mechanical properties of the 2297 alloy plates decreased after solution treatment at 535℃ for 60min and aging treatment at 175℃ for 24 h.(4)The suitable T6 process is 175℃/24h for as-cast 2297 Al-Li alloy(alloy A)after solution treatment at 535℃ for 60min.And the strength of the alloy paltes after typical aging treatment decreases with the increase in the rolling reduction.(5)2297 Al-Li alloy(B alloy)in the original state of T8 treatment was rolled again with different reductions,the optimum aging time and aging temperature increase with the increase of the rolling reductions,but the strength of the plates decreases.The strength decreases more obviously comparing with that of alloy A,which shows that plate in T8 codition is not suitable for rolling again.(6)The main reason why strength of 2297 alloy decreases with increase in rolling reduction is that deformation energy increases and Al3Zr particles became coasin with increase in rolling reduction,which promotes recrystallization.And with increase in rolling reduction the size of T1 phase becomes larger and its density becomes low.