Effect Of Stress Aging On Mechanicalproperties And Microstructures Of 7075aluminum Alloy

The aging forming technology adapts to the developed requirements of low-cost,high-performance in the aircraft body manufacturing field around the world,it provides a new idea of the low-cost manufacturing for airfoil sections and aeroplane wing structures.At the same time,it has also adapted to the background of aircraft researched technologies in China,and has broad application prospects in aviation and aerospace field.On the basis of theory and experiment,we present a study of stress aging of7075-T651 aluminum alloy sheets,including characteristics of stress aging,the effect of stress on aging microstructure and properties of aluminum alloys sheets.In order to carry out such a study,it is necessary to use some experimental technique able to characterizethecompositionofprecipitatesquantitatively,suchas OM,XRD,SEM/EDS,TEM/HRTEM.According to stress-free aging and aging forming comparative study,this paper obtained the characteristics of stress aging and analyzed the effects of stress-ageing forming form-ability and performance.The results show that stress aging has little effect on the grains,coarse phases(Al₂₃CuFe₄)and disperse phases(Al₁₈Cr₂Mg₃)size and morphology of aluminum alloy,but it has great effect on age-forming precipitates.On the one hand,initial strain introduced defect is good for precipitates nucleation,on the other hand,it is good for precipitates growth and grain boundary discontinuity,additionally,the PFZ is clearly width.Initial strain introduced is not only induces preferred oriented of precipitates,but also conducive to precipitates non-nucleation.Thought initial strain introduced is beneficial to aging form-ability,the yield strength and tensile strength of the alloy is decrease and its plasticity and corrosion resistance are improve to some extent.According to comparing the microstructure and properties of the aging forming sheets under different bending radius,this paper obtained the effects of different stress levels on the stress aging properties of aluminum alloy.The results show that with decreasing of pre-bending radius,the yield strength and tensile strength of the alloy increase,the elongation decrease,its plasticity is decrease.The pre-bending radius has little effect on the grains.With the increasing of pre-deformation degree,the quantity of matrix precipitates quantity is more and the size of matrix precipitates is bigger,it is obvious thatηphase become grow and coarse,and also the grain boundary precipitate is coarsening and the precipitate free zone is wide.Through the comparative study of the microstructure and properties of the stress or compression part of the aging forming sheets,it was found that the properties of the alloy in the tensile and compressive parts were significantly different under the same stress level.The yield strength,tensile strength and elongation of the alloy in the compressive stress parts are greater than those of tensile stress parts,but the elongation of the alloy is not much increased.Its microstructures is characterized by transmission electron microscopy（TEM）,it show that the tensile stress and compressive stress can promote the growth and coarsening of large size phase and rod-likeηphase,and the effect of tensile stress is more obvious than that of compressive stress.