High Temperature Plastic Deformation Behavior And Microstructure Simulation Of Spray Formed 7055 Aluminum Alloy

The thermal-mechanical deformation behavior and corresponding microstructural evolution of spray formed 7055 aluminum alloy were investigated.A constitutive model with microstructure evolution model for this material was established.Based on the secondary development of the DEFORM commercial finite element software,the reliability of the developed models was validated,which is meaningful to optimize the hot processing technology of spray formed 7055 aluminum alloy.In this study,a thermo-mechanical simulator by a series of isothermal and constant strain-rate compression tests at deformation temperatures ranging from 380?to 440?and strain rates ranging from 0.1s^-1to 15s^-1 was implemented,by which the high temperature flow stress-strain curves were obtained.Through the analysis of these curves,a constitutive equation describing different flow stages of spray formed 7055aluminum alloy was proposed.The microstructure was observed and analyzed by using of equipment including optical microscope,scanning electron microscope(SEM),electron back scattered diffraction(EBSD),etc.The secondary development DEFORM software was used to simulate the hot compression of the material for the validation of the developed models.The main research conclusions are as follows:(1)In the process of hot deformation of spray formed 7055 aluminum alloy,when dynamic aging occurs,the value of flow stress reaches the local peak and then tends to steady state.When the dynamic recrystallization occurs,the flow stress will decrease obviously after it reaches the peak value,and then presents a gradually increasing trend.(2)A piecewise flow stress constitutive model determined by ln Z value and temperature as critical conditions was established for fitting the true stress-strain experimental data.By comparison,the average relative error between the calculated value and the experimental value is 7.84%,which confirms the reliability of the model until a new steady achieves.(3)The dynamic recrystallization of spray formed 7055 aluminum alloy occurs when the temperature T?683K and the ln Z?29.4,and the dynamic recrystallization volume fraction will increase with the decrease of the value of ln Z.The precipitated MgZn₂ particles dissolved with the increase of temperature during hot deformation process.(4)With the decrease of ln Z value,the proportion of low angle grain boundaries in the deformed microstructure decreases,while the proportion of high angle grain boundaries increases and the dynamic recrystallization degree becomes more sufficient.The grain orientation density along characteristic lattice plane varies with different hot deformation parameters.Vickers hardness research shows that the microhardness value of 7055 aluminum alloy increases with the increase of deformation temperature and decreases with the decrease of strain rate.(5)A hot compressive simulation for the studied material was implemented based on the secondary developed for the DEFORM software.And,the predictions of flow stress and recrystallization behaviors from FE simulation are basically equal to that from the developed model.The prediction accuracy from the proposed model is satisfactory.