Investigation On The Hot Deformation Behavior And Mechanical Properties Of 1420 Al-Li Extruded Bars At Room And Cryogenic Temperatures

With the development of China’s aerospace industry,advanced aircraft,launch vehicles,spacecraft,and other high-end launch equipment have more stringent requirements for lightweight structural components.Al-Li alloy is one of the most promising metal structural materials in the aerospace field due to its low density,high elastic modulus,high specific strength,high specific stiffness,low-temperature resistance,and excellent welding performance.Due to the poor plasticity of Al-Li alloy at room temperature,hot extrusion is an important forming method to obtain thin-walled and multi-cavity Al-Li alloy profiles.However,compared with traditional aluminum alloy,Al-Li alloy is more sensitive to extrusion temperature,deformation rate,and other process parameters.Its forming process window is narrow and improper process parameters easily lead to microstructure deterioration and property degradation.In addition,the special service environment in the aerospace field puts forward higher requirements for the cryogenic mechanical properties of its structural parts.Therefore,it is urgent to carry out the research on the hot flow behavior and microstructure evolution of hot extrusion parts of Al-Li alloy,and systematically analyze its cryogenic mechanical properties,so as to provide theoretical support for the reasonable formulation of the hot forming process.In this paper,the 1420 Al-Li alloy used in alloy aerospace material was the research object,and the method of combining theoretical analysis and experimental tests was used.The high-temperature flow behavior of 1420 Al-Li alloy,the microstructure evolution law of the hot forming process,and the mechanical properties of extruded bars at room and cryogenic temperatures were studied.The main research contents are as follows:(1)Based on the true stress and strain data in the strain rate of 0.0001～10s-1 and the temperature of 300～450℃,the strain-compensated Arrhenius model of 1420 Al-Li alloy and the improved Johnson-Cook model were constructed.The hot processing maps of 1420 Al-Li alloy were established with the evolution characteristics of the microstructure.(2)The extrusion experiments of 1420 Al-Li alloy bars at different extrusion temperatures and speeds were carried out.The extruded bars were treated with solution treatment and aging treatment.Based on EBSD technology,the effect of processing conditions on the grain morphology,orientation distribution,and microstructure of extruded profiles was studied.(3)Uniaxial tensile tests of 1420 Al-Li alloy bars were carried out at room temperature,-40℃ and-196℃.Combined with SEM observation,the mechanical properties and fracture characteristics of 1420 Al-Li alloy bars at room and cryogenic temperatures were studied.