Research On Mechanical Property And Microstructure Evolution In Hot Working Of7085Aluminum Alloy

7085aluminum alloy was developed by Alcoa in2003, it can be thought as thefourth generation of ultra-high-strength aluminum alloy. The alloy has some advantagessuch as high strength, good resistance to stress corrosion and exfoliation corrosionresistance, good ductility and excellent hardenability and cast resistance, etc. The alloyprimarily used in aviation main load-bearing structural components for military aircraftand aerospace equipment and facilities.In this paper, the thermal simulation equipment Gleeble1500was used to do theisothermal compression experiments of7085aluminum alloy.7085aluminum alloy wasdeformed at temperature of250℃,300℃,350℃,400℃,450℃and strain rate of0.01s-1,0.1s-1,1s-1,10s-1. We studied the effect of the deformation conditions on theflow stress, microstructure and thermal processing performance of the alloy. Theprocessing map was established under different deformation conditions. The opticalmicroscopy, field emission scanning electron microscopy and transmission electronmicroscopy were used to analysis the change of the microstructure after deformationand the microstructure corresponding region in the processing maps. The results of hightemperature plastic deformation behavior were used to optimize the forging process of7085aluminum alloy and improve the forging step pass rate. The main results obtainedin this topic are as follows:7085aluminum alloy has steady rheological characteristics and a trend to dynamicsoftening in isothermal compression process. The alloy has positive strain sensitivity.Peak flow stress and peak strain of the material gradually increased with strain rateincreasing; the peak stress and peak strain materials are gradually reduced with thedeformation temperature increasing. A flow stress constitutive equation and a modifiedformula for dynamic deformation activation energy were established. The dynamicrecrystallization critical condition was determined for the alloy which is proportional tothe value of the Z parameter.The microstructure of7085aluminum alloy during hot deformation shows that thedynamic recovery is the main characteristics up to350℃and dynamic recrystallizationabove400℃. The reasons for softening of the alloy are dynamic recovery, dynamicrecrystallization, coarsening of the second particles and flow instability. The mechanismof dynamic recovery mechanism for the alloy is screw dislocation cross slip and climbing; the mechanisms of dynamic recrystallization for the alloy are grain boundarybow out and the rotation, merge and growth of the sub-grain.In this paper, Z parameters was only used a reference for dynamic recrystallizationoccurring or not but not as a condition of judgment for softening mechanism of alloysduring hot deformation, especially in terms similar to the Z parameters, and deformationtemperature impact dynamic recrystallization greater. Under the experimentalconditions, dynamic softening mechanisms are dynamic recrystallization and dynamicrecovery, as well as a dynamic second phase particles precipitate coarsening when thealloy deformed at high Z parameters. The precipitated second phase particles inhibitdynamic recrystallization occurs. The size of the second phase particles increases with Zparameters decreasing, but the density decreases with Z parameter increasing.The processing maps of7085aluminum alloy at different strain were obtained. Theprocessing maps show that the strain has a greater impact on rheological instability area.Rheological instability region tends to increase with the strain increasing, while thesecurity zone has a decreasing trend, that is, there is trend that the safe area convert torheological instability region with the strain increasing. Power dissipation coefficientchanged little, showing little effect of strain on the power dissipation factor.The processing map for the whole hot deformation of the7085aluminum alloywas obtained. The microstructure corresponding with each region of the superimposedprocessing map was analyzed. The microstructure indicates that the characteristic of theinstability region is flow localization and the characteristic of safe area is dynamicrecrystallization. The safe domain in the superimposed processing map is considered tobe the optimum processing area, and the optimized process parameters for the alloy istemperature of380℃-450℃and strain rate range of0.01s-1-0.1s-1.The processing technology depending on the safety area was successfully appliedto the industrial production of7085aluminum alloy forgings. The forging process wasoptimized and the forging step pass rate increased from30%-40%to80%-90%. Thehigh quality forgings were produced and successfully applied to the aerospace field.