| Ultra-high strength Al-Zn-Mg-Cu aluminum alloy is one of the key structural materials indispensable in fields of aerospacedue because of its excellent comprehensive properties,such as excellent specific strength,good hot working and good corrosion resistance.With the rapid development of China's aviation industry,higher requirements are placed on the strength,plasticity,toughness and corrosion resistance of ultra-highstrength aluminum alloys.In order to improve the strength of the alloy,the most direct and effective way is to continuously increase the content of the main alloying elements Zn and Mg,and at the same time combine micro-alloying and suitable preparation process to simultaneously improve the comprehensive properties of the ultra-high strength aluminum alloy.In this paper,the microstructure and mechanical properties of ultra-high strength Al-10Zn-2.5Mg-1.6Cu aluminium alloy were characterized and analyzed by metallographic microscope,scanning electron microscope,transmission electron microscope and tensile test.Based on the systematic study of the influence of Zr and Sc content on the microstructure and properties of hot-rolled sheets,the effect of Sc content on the microstructures and properties of hot-rolled sheets were further studied when Zr and Sc were added together.The mechanism of the effect of trace Zr and Sc on the microstructure of hot-rolled ultra-high strength Al-Zn-Mg-Cu aluminum alloy sheets was revealed.It provides basic data for the development of new ultra-high strength aluminium alloys with strength over 700 MPa and well plasticity,toughness,fatigue and corrosion resistance.The main conclusions are as follows:(1)The size and quantity of T(AlZnMgCu)and Al7Cu2Fe excess crystal phase particles are approximately the same in hot-rolled Al-10Zn-2.5Mg-1.6Cu-xZr/ySc alloy sheets after solid solution treatment followed by water quenching at 465?.There are also Al3Zr dispersion phase particles with the size of 20?40 nm in Al-10Zn-2.5Mg-1.6Cu-(0.046-0.185)Zr alloy.The number of Al3Zr dispersed phase particles increases obviously with the increase of Zr content.When Zr content increases from 0.046%to 0.098%,the size of Al3Zr dispersed phase decreases significantly.No phenomenon of preferential nucleation of the precipitated phase is observed at the interface of the dispersed particles of Al3Zr.There are also Al3Sc dispersion phase particles with the size of 80 nm in Al-10Zn-2.5Mg-1.6Cu-(0.043-0.264)Sc alloy.The increase of Sc content has no significant effect on the quantity and size.There is a phenomenon in which the precipitated phase preferentially nucleates at the interface of the Al3Sc dispersed phase particles.There are also Al3(Sc,Zr)dispersion phase particles with the size of 20 nm in Al-10Zn-2.5Mg-1.6Cu-0.15Zr-(0.034-0.215)Sc alloy.The increase of Sc content has no obvious effect on its size.The amount increases first and then decreases.When the content of Sc is 0.139%,the number reaches the maximum.No precipitation of phase precipitates at the interface of Al3(Sc,Zr)dispersed phase particles.(2)The recrystallized structure and texture of Al-10Zn-2.5Mg-1.6Cu-(0-0.185)Zr alloy sheets are obviously different after solution treatment followed by water quenching at 465?for 1 h and aging at 120? for 24 h.Complete recrystallization occured in both Zr-free and 0.046%Zn alloy sheets,the grain size of which is refined from 50 ?m to 27?m and the surface grains have no obvious preferred orientation,the center of the alloy sheet containing 0.046%Zr contains Cube texture.When Zr content increases to 0.098%,the surface of the alloy sheet is completely recrystallized,and the grain is about 22 ?m equiaxed crystal with no obvious preferred orientation.The core of the sheet is partially recrystallized,and the recrystallized grains and fibrous grains are distributed along the rolling direction.The sheet has obvious Brass texture and weak S,Cube and Copper texture.The surface of the alloy sheet with Zr content of 0.151%is partially recrystallized,the grains have weak Rotated-Cubic,Copper and S orientations,while the core is not recrystallized,and the grains have strong Copper,Brass and S orientation.When Zr content exceeds 0.185%,the alloy sheets are not recrystallized,the grains are fibrous,the surface layer grains of the alloy sheet have extremely strong Rotated-Cubic orientation,and the core grains have strong Brass,Goss,S and Copper orientation.(3)The recrystallized structure of Al-10Zn-2.5Mg-1.6Cu-(0-0.264)Sc alloy sheets are obviously different after solution followed by water quenching at 465? for 1 h and aging at 120? for 24 h.Complete recrystallization occured in both Sc-free and 0.043%Sc alloy sheets,the grain size of which is 50 ?m and 27 ?m,respectively.When Sc content increases to 0.087%?0.133%and 0.192%,the degree of recrystallization of the alloy sheets is reduced,and the sheets are partially recrystallized.The surface of the sheets is equiaxed crystallization with size of 28 ?m,24 ?m and 16 ?m,respectively,while the core of the sheets is fibrous.When the Sc content increases to 0.264%,the degree of recrystallization of the sheets is increased,and the equiaxed size is about 20 ?m.(4)Al-10Zn-2.5Mg-1.6Cu-0.15Zr-(0-0.215)Sc alloy sheets are completely recrystallized after solution treatment followed by water quenching at 465? for 1 h and aging at 120? for 24 h.Complete recrystallization occurs in Sc-free alloy sheets,grain size of which is 50 ?m.When Sc content varies from 0.034%to 0.139%,the alloy sheets are not recrystallized.When the content of Sc exceeds 0.189%,the recrystallization occurs in the alloy sheets.With the increase of Sc content,the recrystallized grains are extremely small.(5)After solution treatment followed by water quenching at 465? and aging at 120?for 24 h,the strength of Al-10Zn-2.5Mg-1.6Cu alloy sheet increases with the increase of Zr and Sc content,and the elongation increases at first and then decreases with the increase of Zr or Sc content.(6)The optimum Zr and Sc contents in Al-10Zn-2.5Mg-1.6Cu alloy are 0.151%and 0.133%respectively.The corresponding optimal solution process is heating at 465? for 1 h.The comprehensive properties of the sheet are the best after aging at 120? for 24 h.The tensile strength,yield strength and elongation of Al-10Zn-2.5Mg-1.6Cu-0.151Zr and Al-10Zn-2.5Mg-1.6Cu-0.133Sc alloy sheets are 704 MPa,645 MPa,10.3%and 654 MPa,591 MPa,9.3%,respectively.(7)The optimum Sc content in Al-10Zn-2.5Mg-1.6Cu-0.15Zr alloy is 0.139%,and the corresponding optimum solid solution process is heating at 465? for 1h.The comprehensive properties of the sheet are the best after ageing at 120? for 24 h.Its tensile strength,yield strength and elongation are 701 MPa,665 MPa and 8.0%,respectively. |
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