Study On Dislocation Density And Microstructure Evolution Of Hot Working Process Of 7A85 Aluminum Alloy

7A85 aluminum alloy has been widely used in the manufacture of aviation die forgings due to its high strength,high fracture toughness and high hardenability.During the forming process of aluminum forgings,the microstructure of the material is determined by the thermal deformation and heat treatment process,and ultimately determine the comprehensive performance.During the process,the flow behavior of the material is affects by the dislocation density,and the microstructure evolution also has a great correlation dislocation density.Therefore,the study on the evolution of dislocations in the whole process of thermal deformation and heat treatment of 7A85 aluminum alloy has practical significance for predicting the microstructure and performance of aluminum alloy.Firstly,the flow behavior of 7A85 aluminum alloy was studied by isothermal compression test at the strain rate range of 0.001s^-10.5s^-1 and temperature range of250⁴50°C.The dislocation evolution law of the alloy during plastic deformation is investigated.Based on the difference of the softening mechanism before and after the peak stress,a“Two-stage”Kocks-Mecking?K-M?dislocation density model was established to describe the dislocation evolution during the plastic deformation process of 7A85aluminum alloy,and the accuracy of the model was verified.Secondly,optical microscopy?OM?and electron backscatter diffraction?EBSD?analysis was carried out to the study the effects of deformation temperature and strain rate on microstructure such as grain size and grain boundary orientation angle.The mechanism of microstructure evolution under different deformation parameters was revealed,and the dynamic recrystallization grain size evolution model of 7A85 aluminum alloy was also obtained by linear regression.Finally,the hot compressed specimens of 7A85 aluminum alloy after were solution and aging treated at different conditions,and then the dislocation density at different aging time and different aging temperatures was analyzed by XRD linear analysis.The effect of aging time and aging temperature on the evolution of dislocation density was revealed.The microstructure of 7A85 aluminum alloy after aging treatment was observed by transmission electron microscopy,the dislocation evolution of aluminum alloy during aging process was further revealed.