High-throughput Composition Optimization Design And Experimental Study Of New Lightweight And High-strength Aluminum-lithium Alloy

The aluminum-lithium alloys are one of the most competitive light high-strength materials in the aerospace field,with low density,high ratio strength and high modulus.With the increasing needs of large-scale and lightweight of aerospace equipment,higher requirements are put forward for the comprehensive performance of Al-Li alloys,and it is urgent to develop new high-performance Al-Li alloys.Due to the large number of Al-Li alloy elements and complex composition,discrete control of single alloy composition through"trial and error method"not only has a long cycle,time consumption,but also is difficult to comprehensively consider and improve the performance of Al-Li alloy,which can not meet the needs of precise composition design of Al-Li alloy with high comprehensive performance.In view of the above problems,this paper proposes and constructs a method of the high-throughput composition optimization design of Al-Li alloys.By combining CALPHAD（phase diagram calculation）method and the secondary development of thermodynamic calculation database,the key properties/properties of the alloy were calculated in batches and the composition of the target alloy was screened.Furthermore,Pandat software was used to design the heat treatment process of the alloy,and the synergistic design of the alloy performance improvement and process optimization was realized.The alloy with optimum composition was prepared by experiments,and the accuracy of design method and model was verified.The main conclusions are as follows:（1）The effects of main and microalloying elements on the equilibrium precipitates and thermodynamic properties of the alloy were studied.The results show that:Cu,Li and Mg significantly increased the content of T₁phase.In the range of 2.5wt.%～5.5wt.%Cu,the content of T₁ increased with the increase of Cu content,and the peak content of T₁ reached 9.4%.The solidification interval of the alloy increased,and the solid solution window of T₁ phase decreased.Li changed the solidification path and precipitation sequence of the alloy,and the precipitation range of T₁ phase was 1.0wt.%～2.5wt.%Li.In the range of 0.2wt.%～0.8wt.%Zn,the content of T phase（Al Li Zn₂）increases from 0.5%to 2.0%,which is unfavorable to the plasticity.At 0.3wt.%Mn,Al₂₀Cu₂Mn₃ dispersion does not compete with Cu atoms in T₁ phase.Zr content affects the liquidus temperature of the alloy.In the range of 0.05wt.%～0.25wt.%Zr,Al₃Zr phase content and liquidus temperature increase with the increase of Zr content.The optimized alloy composition space was Al-（2.5～4.5）Cu-（1.0～2.5）Li-（0.4～0.8）Mg-（0.1～0.3）Ag-（0.1～0.2）Zr-0.2Zn-0.3Mn.（2）Based on the experimental data and simulation results,a quantitative model of the relationship between alloy composition and solid temperature was established,and the density regression model of Al-Cu-Li alloy was revised.Based on the design objective,four basic microstructure parameters were selected as screening conditions:volume fraction of T₁phase（≥6.0%）,solution window（≥45℃）,solidification interval（≤190℃）and density（≤2.72g/cm³）.（3）The automatic batch calculation and screening of key properties/properties of Al-Li alloy were realized by writing the alloy composition file using MATLAB programming language.The optimal alloy composition was Al-3.7Cu-1.3Li-0.8mg-0.1Ag-0.3Mn-0.2Zn-0.1Zr.Furthermore,the precipitation kinetic parameters（kdb）file of Al-Cu-Li alloy was developed by Pandat software,and the precipitation simulation of the designed alloy was carried out.The optimal heat treatment process was determined as 510℃solution/1h+180℃/20h aging..（4）The optimum composition alloy was prepared and its density was measured,the phase transition law was verified and the microstructure of T₁ phase was characterized.The results show that the room temperature density of the alloy is 2.642g/cm³,and the peak temperature of T₁ phase is495.98℃,which is close to the calculation results of phase diagram.After aging treatment,the size and quantity of T₁ phase in the alloy increase significantly,and the distribution is more uniform,becoming the main strengthening phase,indicating that the microstructure and properties of the alloy meet the expected design objectives,and verifying the reliability of phase diagram calculation and high-throughput composition design process of the alloy.