| Al-Cu-Mg-Ag alloy has the characteristics of higher specific strength,perfect thermal stability,excellent corrosion resistance,easy to get and cost-effective.It is quite suitable for the demand of civil supersonic aviation aircraft in the future.And It has a great development prospect.The higher temperature creep test can well simulate the service state of the alloy during supersonic flight.The steady creep rate and creep rupture time are two important parameters to measure the creep properties of the alloy.In this experiment,Al-5.3Cu-0.4Mg-0.4Ag-0.3Mn-0.1Ti was used as the fundamental alloy,and two kinds of tested alloys were prepared by melting and casting:The Al-Cu-Mg-Ag-Mn-Ti-xZr alloy with different Zr content?0,0.15,0.25,0.3,0.35 wt.%?had been made.The mechanical properties at room temperature and creep properties under higher temperature of the tested alloys with under-aged?180°C/8 h?treated were studied.And the creep behavior of the alloy was mathematically fitted by the creep constitutive equation??=Anexp?-Q/RT??;The Al-xCu-Mg-Ag-Mn-Ti-Zr-Sc alloy with different Cu content?5.23,5.56,5.82 wt.%?had been made.The mechanical properties of the test alloy at room temperature and the high temperature creep behavior of the under-aged alloy were investigated.Besides,the creep behavior of the alloy was mathematically fitted by the creep constitutive equation.The results showed that:?1?The addition of Zr could significantly improve the tensile strength of the test alloy at room temperature.The alloy with 0.35 wt.%Zr content under the condition of180°C/8 h aging had the best tensile strength at room temperature.And it was tiny that the difference of mechanical properties between alloy with 0.15 and 0.35 Zr content,the alloy with 0.25wt.%Zr content was the worst.But the alloy with Zr content still had the advantage of mechanical properties.The tensile strength,yield strength and elongation of the alloy with 0.35wt.%Zr content were 455.52 MPa,387.29 MPa and11.61%respectively.Compared with the Zr-free alloy,the tensile strength had increased by 9.29%,the yield strength had increased by 14.83%,and the elongation had reduced by 16.77%.?2?Under the conditions of 200?/150 MPa and 200?/200 MPa,the creep behavior of the alloy with higher Zr content had the advantage.The alloy with 0.35wt.%Zr content had the lowest steady creep rate after 100 h creep test,and the creep strain of the alloy was the smallest too,it was showing the most excellent creep performance.A series of creep tests were studied at 200?with different stress of 250 MPa and 300MPa,and at 200 MPa with different temperature of 240?and 260?,the tested alloy without Zr content always had the best creep performance,the addition of Zr weakened the creep properties of the alloy.Under the conditions of higher temperature and higher stress,this phenomenon was more obvious.The creep rupture time of the test alloy with 0 wt.%Zr content under the condition of 200°C/300 MPa was 70.01 h,which was2.68 times of the alloy with 0.35 wt.%Zr content,and the creep rupture time of Zr-free alloy at 260°C/200 MPa was 15.99 h,which was 2.35 times of the alloy with 0.35 wt.%Zr content.?3?The increase of Cu content?5.23?5.56?5.82wt.%?did not have a significant effect on the tensile properties of the tested alloy,under the aging condition of 180?for different hours?8,12,14 h?,at room temperature.Under the room temperature,the statistical analysis of the yield strength,tensile strength and elongation of the three test alloys under different aging conditions showed that the statistical average of yield strength,tensile strength and elongation were 374.3±29.3 MPa,453.5±24.43 MPa and10.2±1.07%respectively.Due to the same Zr and Sc content of the three test alloys,a large number of aging-insensitive deformation W-phase?AlCuScZr?with dispersion strengthened in the alloy caused the test results.?4?The increase of Cu content?5.23?5.56?5.82wt.%?had a great influence on the creep properties of the test alloy.The tested alloy with 5.82wt.%Cu content always had the best creep performance,and this phenomenon was more obvious in the conditions of higher temperature and higher stress.Under the condition of 240°C/200MPa,the creep rupture time of the alloy with 5.82wt.%Cu content was 64.43 h,which was about three times of others.Under the condition of 200°C/250 MPa,the steady creep rate of the alloy with 5.82wt.%Cu content was 6.31×10-7s-1,which was only 30percent of others.?5?The high resolution TEM photographs of?phase showed that the precipitation and growth of?phase was the results of atom diffusion,it was a diffusion transformation.It was small that the lattice mismatch between?and the matrix,which could effectively improve the thermal stability of the alloy.The phase of??had a similar effect too.The?phase of the alloy was severely coarsening after the creep test under the condition of 260°C/200 MPa.The thickness of?is about 2 nm before the creep test,and after the creep test the thickness of?had reached about 5 nm.The coarsening of?led to a decrease on the thermal stability of the alloy.During this process,a large number of solute atoms segregation occurred in the grain boundary of the tested alloy.The precipitation free zone?PFZ?near the grain boundary became wider.Before the creep test the width of PFZ was 200 nm,and doubles after the creep test,and it reached about 400 nm. |
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