Research On Hot Deformation Behavior, Mechanical Properties And Microstructure Of High Strength Al-Zn-Mg-Cu Alloy

The hot deformation behavior and microstructure evolution of high strength aluminum alloys Zn11.0-Mg(2.3-3.6)-Cu(0.4-1.5)were systematically studied.The processing maps of alloys were established,and the microstructure and properties of high strength as-extrude aluminum alloy under different aging conditions were also studied.The main research contents are as follows: The hot deformation behavior of five kinds of high strength aluminum alloys was studied by Gleeble-1500 D hot-simulation machine.Their constitutive equations under hot deformation and processing maps were established.The suitable processing window of high strength aluminum alloy was acquired.The microstructure evolution during hot deformation was systematically studied by EBSD and SEM techniques.The tensile properties of as-extrude sheet under different aging processes were tested and their microstructure were studied by TEM,and their strengthening mechanism was analysied The results shown that the hot deformation process of high-strength aluminum alloys contain four stages,namely the hardening stage,the dynamic softening stage,the steady-state rheological stage and the continuous hardening stage.The Arrhenius constitutive equation which have consideredthe strain compensation can predict the rheological behavior of the alloy well.The suitable processing temperature and strain rate range of the high strength aluminum alloys studied is 360? to 420 ? and 0.003s-1 to 0.03s-1 respectively.The composition of main alloying elements has a significant effect on the rheological behavior.With the decrease of Mg content,the instability zone is reduced and the energy dissipation peak decreases.With the decrease of Cu content,the instability zone increases and The peak region of energy dissipation coefficient shrinks to the high temperature and low strain rate region The rheological instability zone is expanded to the whole deformation temperature range,and the peak value of the energy dissipation coefficient increases with the strain of the strain rate.The change of the energy dissipation coefficient in the safe zone is related to the solution of ? phase(Mg Zn2).The results on microstructure analysis of deformed samples show that the relative amount of the dynamic recrystallization increases with the increase of the deformation temperature.The relative amount of the dynamic recrystallization decreases with the increasing strain rate.The main softening mechanism of high strength aluminum alloy during hot deformation is dynamic recovery,and there is a small amount of dynamic recrystallization.The content of Mg,Cu in the alloy have little effect on the amount of sub-crystal structure,and have a great influence on the relative amount of the recrystallized structure.The relative amount of recrystallized structure decreases with the decrease of Mg,and increases with the decrease of Cu.The study on the microstructure and properties of high strength aluminum alloy extruded sheet show that their main strengthen phase is ?' phase.At the early stage of aging period,a certain amount of GP zone and ?' phase formed.With the increase of aging time,the size of ?' phase increases gradually while their number of density decreases some of the ?' phase transformed into ? phase.The yield strength and tensile strength of 7#(Al-11.55Zn-2.05Mg-2.05Cu-0.09Zr-0.22Sc)alloy under 110?/8h+145?/4h aging process can reach 745 MPa and 755 Mpa respectivelyand the elongation is 8.6%,which was to obtain a good strong plastic match.