Effect Of Initial Blank Tissue State On The Anisotropic Behavior Of 2195 Aluminum-lithium Alloy Creep Aging

Aluminum-lithium alloy is light in weight and high in modulus.It is the most promising lightweight and high-strength aluminum alloy material in the modern aerospace field.The anisotropic difference in deformation and mechanical properties during its forming process is the key to restricting its high performance and precise forming.one of the problems.In this paper,taking 2195 aluminum-lithium alloy as the research object,according to its anisotropic characteristics during the creep-aging forming process,the influence of the initial billet state on the creep-aging anisotropic behavior of aluminum-lithium alloy is studied.The main research contents are as follows:（1）The effects of three initial precipitation states of solid solution state,natural aging state and peak aging state on the creep-aging plane anisotropy behavior of 2195 aluminum-lithium alloy were studied.It was found that the initial mechanical properties of 2195 aluminum-lithium alloy with different precipitation phase states.The laws of property anisotropy are similar,and the strengths all show a trend along the rolling direction（S0）>vertical rolling direction（S90）>45 degrees（S45）,and the elongation at S45 is the highest.The creep aging test results of 2195aluminum-lithium alloy billets under different initial precipitation phases with equal stress-yield ratio show that:when there is no precipitation phase or a small amount of precipitation phase,the creep strain curves in the three directions almost overlap,and the creep anisotropy is not obvious;The three-direction creep strain in the state of a large number of precipitates is in the order of S90>S45>S0,showing obvious anisotropy.The reason for this phenomenon is the uneven precipitation of the main strengthening phase T₁ phase.After creep aging with equal stress yield ratio,the initial state is solid solution state（no precipitate phase）or natural aging state（a small amount of precipitate phase）,the size of T₁ phase is similar,but after artificial aging,the size of T₁ phase of S0 is larger than that of S45 and S45.S90.When the initial state is the peak aging state（a large number of precipitated phases）,the size of the T₁ phase in the S0 direction after creep is still slightly larger than that of S45 and S90.（2）Three kinds of 2195 aluminum-lithium alloys with different initial dislocation densities were obtained by pre-stretching 0%,4%and 8%of the naturally aged 2195 aluminum-lithium alloy,and their dislocation densities were 3.927×10¹⁴m^-2.8.409×10¹⁴m^-2 and 8.835×10¹⁴m^-2;with the increase of pre-deformation,the dislocation density increases,which greatly improves the initial yield strength of the material,but the elongation decreases to a certain extent,which increases the anisotropy of mechanical properties.The creep aging test results of equal stress yield ratio under the three initial dislocation densities show that the anisotropy of the creep strain at steady state increases with the increase of dislocation density,and there is a pre-deformed billet in the creep aging process.The"multi-stage"phenomenon of the creep strain curve disappears,and the creep strain anisotropy decreases.After creep aging,the size of T₁ phase of S0 is larger than that of S45 and S90,and dislocations promote the anisotropy of precipitation speed and precipitation size of T₁ phase in different directions.However,the anisotropy of mechanical properties decreased significantly after creep aging.（3）In summary,different microstructure states of the billet affect the anisotropic behavior of the 2195 aluminum-lithium alloy by affecting the precipitation behavior of the T₁ phase during the creep aging process.Combined with the mechanical properties and creep strain anisotropy characteristics of 2195 aluminum-lithium alloy,and on the basis of considering the microscopic variables such as dislocation density,precipitate size,precipitate shape factor,and precipitate volume fraction,a model that can describe the microstructure of the initial billet is established.The macro-micro unified constitutive equation of the creep aging anisotropy of 2195 aluminum-lithium alloy affected by the influence,realizes the prediction of yield strength and creep strain during creep aging at different stress levels and different directions,and the prediction deviation of yield strength is less than 5.4%,the creep prediction deviation is less than 7.8%,which proves the accuracy of the anisotropic constitutive equation.Through the finite element simulation and test results of the creep aging process of 2195 aluminum-lithium alloy samples with different billet microstructures,it is shown that when this anisotropic constitutive is used,for 2195-T34 and T6 Al-Li alloys,the creep aging,the final profile prediction accuracy can be increased by 50.2%and 67.7%,respectively.It has good predictability for the anisotropic behavior of 2195 Al-Li alloy during creep age forming under different initial billet microstructures,and can be used to guide different creep aging forming process of 2195 Al-Li alloy in the initial billet microstructure is formulated.