Study On Microstructure,Mechanical Properties And Their Anisotropy Of Al-3Li-1Cu-0.4Mg-0.1Er-0.1Zr Alloy

Although aluminum-lithium alloy has the advantages of low density,high modulus and corrosion resistance,the anisotropy of deformed aluminum-lithium alloy is very serious,which seriously limits the application of aluminum-lithium alloy.With the continuous development of China’s aerospace industry,the strength of aluminum-lithium alloy is also put forward higher requirements.In view of this situation,this paper selects the new aluminum-lithium alloy of Al-3Li-1Cu-0.4Mg-0.1Er-0.1Zr as the research object.In this paper,the influence of hot rolling process on the microstructure,mechanical properties and anisotropy of aluminum-lithium alloy is studied.The rolling process parameters are optimized,the mechanical properties of the alloy are improved,the anisotropy of the mechanical properties of the alloy is reduced,and the relationship among the rolling process,microstructure,mechanical properties and anisotropy of the aluminum-lithium alloy is established.Finally,this paper further explores and optimizes the parameters of solid solution and aging of aluminum-lithium alloy,studies the effect of heat treatment on the microstructure and mechanical properties of the alloy,and further improves the tensile strength of the alloy through heat treatment.In this paper,characterization techniques such as OM,XRD,TEM,SEM and EBSD,as well as testing techniques such as microhardness testing and tensile performance testing,were used to characterize and test different rolled and heat-treated aluminum-lithium alloys.The results show that the second phase distributed along the grain boundary of the alloy cannot be completely eliminated after homogenization.At 500℃,the alloy is subjected to multi-pass hot rolling with 20%,50%and 90%deformation.The results indicate that,with the increase of rolling deformation,the second phase distributed along grain boundaries in the alloy is gradually broken and dissolved.The second phase ultimately transitions from a continuous enrichment distribution at grain boundaries to a more uniform granular distribution in the matrix.The size of the second phase is reduced to the micron or even nanometer level.During the 90%hot rolling process,a large amount of Al₃Li phase and Al₃（Er,Zr,Li）core-shell structure composite phase were precipitated in the alloy,and recrystallization occurred through the PSN（Particles stimulated nucleation）mechanism.After 90%rolling,the strength and plasticity of the alloy have reached the best,with a tensile strength of 362 MPa and an elongation of 19.1%.The unidirectional hot rolling and cross hot rolling of the aluminum-lithium alloy with 90%deformation were carried out,and the influence of the rolling process on the texture and mechanical properties of the alloy were studied.It is found that PSN recrystallization still occurs after cross-rolling of aluminum-lithium alloy,but the number of recrystallized grains is reduced.The texture components of aluminum-lithium alloy after unidirectional rolling are mainly RB texture{011}<111>and brass R texture{111}<112>,while after cross-rolling,the texture component of the alloy is mainly brass R texture{111}<112>.Although the average tensile strength and average elongation of cross-rolled alloys are slightly reduced compared with unidirectional rolled alloys,cross-rolling greatly reduces the anisotropy of mechanical properties.90% unidirectional rolled aluminum-lithium alloy with the highest tensile strength is selected for exploring the process parameters of solid solution and aging,aiming to further improve the mechanical properties of the alloy,especially the tensile strength of the alloy.The results show that the optimal solution and aging process parameters are 560°C/4h solution and200°C/7h aging.After the alloy is soluted at 560°C/4h,the large micron-level second phase in the alloy can be eliminated,the crack source in the alloy can be reduced,and the strength of the alloy after solution is significantly reduced,but the elongation can be increased to 22.1%.After the aging of 200°C/7h,a larger number of Al₃Li phases and core-shell composite phases with finer size and more uniform distribution were precipitated.Although aging reduces the elongation of the alloy,it further improves the tensile strength of the alloy.After solid solution and aging,the tensile strength of the unidirectional rolled alloy increased by 139 MPa,reaching 501 MPa.