| Al-Cu-Mg alloy has low density,good corrosion resistance,good plasticity and good room temperature strength,and is often used as aircraft skin material,but with the development of aviation technology,The supersonic cruising speed of modern supersonic aircraft can reach Mach 2.4 or more,at which time the fuselage skin temperature of the aircraft can reach or exceed 190 °C,and the skin made of 2 series aluminum alloy if exposed to an environment above 150 °C for a long time,the precipitated phase in the alloy will be roughened or phase changed,the microstructure will be damaged,and it is easy to fail,which will cause some accidents.Adding Ag to the alloy can change the precipitation sequence of the second phase in the alloy,so that the θ phase is transformed into a high-temperature resistant Ω phase precipitation,and the addition of Zr can increase the recrystallization resistance of the alloy,so that the alloy retains more deformation structure and improves the performance of the alloy,but the addition of Zr requires a better heat treatment process to cooperate.Based on this,this paper uses the method of calculation combined with experiment to design and improve a 2 series aluminum alloy with good high temperature performance based on 2624 alloy.The design and optimization of the alloy composition is carried out by thermodynamic calculation combined with first-principles calculation,after determining the stable precipitated phase that may be contained in the alloy,the thermal stability and mechanical properties of the precipitated phase are explored by thermodynamic calculation combined with first-principles calculation,and after calculation,it can be used as the heat-resistant strengthening phase of the alloy with the T phase,the Al3 Zr phase and the θ phase that will be replaced by the Ω phase later.The influence of Cu,Mg,Mn,Zn,Zr and other elements in the alloy on the precipitated phase in the alloy is studied by thermodynamic calculation to determine the content range of each element in the alloy,the Ag content range is determined by studying the influence of Ag content on the alloy matrix by virtual crystal approximation,and the alloy composition obtained by calculating is Al-4Cu-0.4Mg-0.5Mn-0.5Zn-0.4Ag-x Zr,of which the Zr content is set to four component points,which are 0wt.%,0.08 wt.%,0.16 wt.% and 0.24 wt.%.Based on the calculated alloy composition,four alloys with regard to the change of Zr content were cast,and the heat treatment process of these four alloys was explored based on the actual composition of the cast alloy.The diffusion ability of each element in the alloy in the Al matrix was studied by first-principles calculation,and the phase diagram of the four alloy components,the influence of homogenization temperature on the concentration distribution between the secondary dendrite arms of the alloy,the TTT and CCT curves,and the aging time and temperature on the precipitated phase were calculated by thermodynamic calculation.Using tensile test and various microscopic characterization methods to optimize and verify the calculated results,it is found that Al-4.31Cu-0.5Mg-0.34Ag-0.42Zn-0.53Mn-0.15 Zr alloy has the best room temperature and high temperature mechanical properties among the four alloys after 420°C/8h+510°C/16 h homogenization treatment,510°C/1.5h solid solution treatment and 190°C/3h aging treatment lag,and it is found that it has the smallest dispersed Ωphase and Al3 Zr phase by TEM means,and the diffuse distribution Al3 Zr phase can promote the heterogeneous nucleation of the Ω phase and promote its precipitation,can also reduce the width of the alloy PFZ(no diffusion precipitation band)and improve the alloy properties. |
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