Study On Anisotropy And Fatigue Properties Of 2297-T87 Al-Li Alloy Thick Plate

2297 Al-Li alloy is the third-generation Al-Li alloy which was developed by American at the end of the 20th century.The alloy has medium specific strength and high damage tolerance.The main application specification in aerospace field is 2297-T87 thick plate,and the product thickness is usually between 40-150mm.With the addition of Li element,the aluminum alloy has obvious anisotropy along with its mechanical properties,which is mainly reflected in the anisotropy of the mechanical properties and the non-uniformity of the thickness of the thick plate,which seriously hinders the development and application of Al-Li alloys.Therefore it's very meaningful to conduct in-depth research on relevant issues,to explore its influencing factors and to seek ways to reduce the degree of anisotropy,which can further promote its application in the aerospace industy.Optical microscopy(OM),electron back-scatter diffraction(EBSD),scan electron microscopy(TEM)and tensile testing were performed to investigate the inhomogeneity,anisotropy of mechanical properties and fatigue properties of 2297 Al-Li Alloy thick plate.The main conclusions were drawn as follow:The textures of 45mm,85mm and 95mm thick plates are all dominated by S texture,and recrystallization texture is found at the center of 45mm thick plate;At(D/4,W/2),85mm and 95mm thick plates are dominated by recrystallized texture,where the 45mm thick plate is dominated by shear texture;At(D/2,W/2),the 85mm and 95mm thick plates are dominated by a shear texture,where the 45mm thick is the brass texture;The texture composition of 85mm and 95mm thick plates at different locations is consistent,which is different from that of 45mm thick plate.In the 1/4 thickness layer,the fracture modes in the L-,LT-,and 45-directions are mainly intergranular fractures with plasticity,and the ST-direction is mainly brittle fractures.The anisotropy of the mechanical properties is as follows:the strength in the LT direction is the highest,the L direction is the second,the strength in the ST direction is the lowest,the direction of the 45° direction is not significantly different from the L direction,and slightly lower than the L direction;the elongation in the L direction and the 45° direction is the highest.The direction of LT followed,and the extension rate of ST was the lowest.With the increase of stress levels,the cycle of fatigue cycles is significantly reduced;the increase in ambient temperature also leads to a significant decrease in cycle times.When the same temperature and the same load strength,its fatigue has obvious anisotropy with the direction,the law is:Fatigue property in LT direction is the best,followed by ST direction and L direction is the worst..The fatigue crack initiation of 2297 Al-Li alloy occurs mainly on the surface of the sample,the inclusions in the near surface and the grain boundary.In the process of crack propagation,the propagation path of LT to the crack is more tortuous than that of L,and the ST direction has typical cleavage characteristics.The morphology of the fault zone is similar to that of static tensile.The L direction and LT are the intergranular fracture which belongs to the plastic fracture,and the ST direction is the brittle mode.