The Research On Thermal Deformation Characteristics And Rolling Processing Of7050Aluminum Alloy

In order to make breakthroughs in key technologies for the processing of highstrength and high toughness aluminum alloy, and to obtain for enterprise productionprocess, optical microscope, scanning electron microscope, X-ray diffraction and tensilemechanical properties testing were adopted to study the high-temperature rheologicalcharacteristics, evolution of the microstructure during hot compression deformation andeffects of rolling process on the microstructure and mechanical properties of7050aluminum alloy in the condition of physical simulation (Gleeble-1500) and laboratoryrolling.The main results are as follows:①The flow stress was strongly dependent on the deformation temperature and thestrain rate when the samples of7050aluminum alloy were deformed under thecondition that the deformation temperature was within300℃and450℃and the strainrate was within0.01s-1and10s-1. It would decrease with increasing the deformationtemperature and decreasing the strain rate. The hot deformation activation energy Q wascalculated as250.3kJ/mol and the flow stress of7050alumunium alloy could bepresented by Zener-Hollomon Parameter in exponential form as follows:②The processing maps of7050aluminumu alloy had been constructed accordingto dynamical material model, and the safe areas in different hot deformation conditionswere determined to be that the deformation temperature was within400℃and450℃and the strain rate was within0.01s-1and0.1s-1. The results of the microstructurecharacteristics in different deformation conditions showed that only dynamic recoveryoccurred when alloy deformed at300℃and when the temperature reached to400℃,the dynamic recrystallization had occurred and the size of the recrystallized grainswould increase with increasing the temperature, whose softening mechanism alsotransformed to recrystallization from dynamic recovery. Compared to high strain rate,there was enough time for material to deform, which would provide structure andenergy conditions for the nucleation of recrystallization and promote the degree ofrecrystallization. ③Influences of total reduction and pass reduction on the microcture andproperties of7050aluminum alloy were studied through laboratory rolling. The degreeof dynamic recovery would increase and the subgrains would form recrystallized grainsthrough subgrain coalescence nucleation with increasing the degree of rollingdeformation. Overall, the aluminum alloy with the pass reduction of1.5mm and thetotal reduction of50%possessed better comprehensive mechanical properties, whoseyield strength was332MPa, the tensile strength was450MPa and the elongationwas13.3%.④The hot-rolled sheets were solution treated at470℃for1h and aged at121℃for6h and161℃for16h. With the increasing amount of rolling deformation, thedegree of crystallization of the hot-rolled sheet has increased, the microstructurebecame more uniform and the second phase diffusely distributed after aging treatment.Compared with the sample with pass reduction in3.0mm, the recrystallization was moresufficient, the microstructure was more uniform, the grain boundary was much clearerand the number of the second phase decreased in the sample with pass reduction in1.5mm. Results of X-ray diffraction analysis showed that the major second phase wereη (MgZn2) and S (Al2CuMg). The content of precipitates η ’ increased slightly withincreasing the degree of rolling deformation, while the η phase decreased. Withincreasing the total reduction, the intensity of the rolling texture would graduallyincrease and the type of texure transformed from deformation texure to recrystallizationtexure, but the impact of pass reduction on texture was’t obvious. Moreover, themechanical properties of hot-rolled sheet had been improved after aging treatment, itwas that the yield strength had increased by100-180MPa, and the tensile strength hadincreased by40-140MPa. The sample with pass reduction of1.5mm and totaldeformation of70%possessed the best mechanical properties with yield strength of472MPa, tensile strength of544MPa and elongation of14.5%.