Research On Microstructure Evolution And Mechanical Property In Hot Deformation Of Aluminum Lithium Alloy

2195 aluminum-lithium alloy has some advantages such as low density,high modulus of elasticity,high specific strength,excellent forgeability,weldability and low temperature performance,etc.,which is considered to be one of the ideal materials in the design of modern aerospace equipment.Thermoplastic forming and heat treatment are important parts in the alloy manufacturing process.The final microstructure and mechanical properties of the alloy also depend to a great extent on the matching of the forming process and the heat treatment process.Studying on the influence of forming and heat treatment processes on the microstructure and properties of the alloy can further promote its application in the aerospace field.In order to eliminate the segregation of the dendritic components and the low melting point phase in the aluminum-lithium alloy ingot,dissolve the second phase of the high alloy content in the matrix and the grain boundary,and make the solute atom distribution more uniform,first the Al-Li alloy is homogenized by box-type resistance furnace,which is conducive to the follow-up processing.The results show that the suitable homogenization process of 2195 Al-Li alloy is at 490?for 40h.At this time,the coarse non-equilibrium phase in the microstructure of the alloy is basically dissolved,replaced by the dispersive?'phase,and a small amount of?phase remains at the triangular grain boundary.The composition of the structure is relatively uniform,which is suitable for hot working.In order to provide theoretical basis for the formulation of hot working process,further investigate the hot deformation behavior of the alloy and obtain accurate flow stress,constitutive relation and thermal processing map,the hot compression simulation experiment of the homogenized alloy was performed on Gleeble-3800 thermal simulation machine.The constitutive equation and processing map of the 2195 Al-Li alloy were established.The deformation activation energy?Q=226.379 KJ/mol?and other related parameters were obtained.The processing diagram showed that 2195 Al-Li alloy is a strain rate sensitive material,and the rheological instability would occur during hot working at a high strain rate(0.1¹0 s^-1).The technological parameters in the safe working area are:strain rate is between 0.01 and 0.1s^-1,deformation temperature is between 400 and 470?.The dynamic recrystallization occurs and the grains are fine and uniform with the deformation temperature is between 458?and 470?.The hot working process parameters of the alloy are formulated within this region to optimize its processing properties.The intermetallic compound T₁ phase is the main precipitation phase in Al-Li alloy,which plays an important part in improving the strength and toughness of the alloy,and its precipitation also affects the process of dynamic recrystallization.In order to analyze the relationship between the precipitation of T₁ phase and the dynamic recrystallization of alloy during thermal deformation,the microstructure of hot-compressed samples was studied by metallographic microscopy.The results show that the microstructure of the alloy will undergo uneven deformation during the hot compression process,and the re-precipitated T₁ phase is also different due to different regions.With the increase of deformation temperature,the size and number of precipitated T₁ phase are decreasing.This phenomenon's degree of occurrence is also different in different regions.Dynamic recrystallization occurs when the deformation temperature is 460?.This result can provide a basis for the formulation of hot forging processes and the prediction of mechanical properties.Referring to the processing process determined by the thermal processing map,the2195 Al-Li alloy was rolled by a rapid hot rolling test machine with 350 mm wide rolls,and alloy plates were obtained finally.The plates treated by T8 solution ageing treatment has certain anisotropy.The transverse mechanical properties of the rolled sheet is the best,and its tensile strength reaches 451.97 MPa.The tensile strength of longitudinal and 45°direction is 418.03 MPa and 437.10 MPa,respectively.