Research On The Rheological Behavior And Constitutive Model Of AA7075 In Solid Solution State

In recent years,lightweight technology has been increasingly valued in the field of manufacturing.7075 aluminum alloy is an ideal lightweight material because of its low density,high yield ratio,good impact resistance.However,the forming ability of 7075 aluminum alloy is poor at room temperature,the hot stamping technology of aluminum alloy can effectively solve this problem.In the current research on hot forming of aluminum alloy,most of the studies on high temperature constitutive model of 7075 aluminum alloy have not considered the influence of solid solution parameters,or fixed the effect of solid solution as a constant,without considering the influence of thermodynamic history.Therefore,it is of great significance to study the rheological behavior and constitutive model of7075 aluminum alloy in solid solution state to formulate the hot stamping process and improve the accuracy of constitutive model prediction.In this study,the thermal tensile tests were designed with the solid solution temperature,solid solution time and strain rate as variables,and the thermal deformation behavior and microstructure evolution of 7075 aluminum alloy in solid solution state were studied.During the solid solution treatment,the volume fraction of the second phase of 7075 aluminum alloy decreased with the increase of the solid solution temperature and the prolonging of the solid solution time.During the thermal deformation process,the dislocation density of 7075 aluminum alloy increased with the increase of solution temperature and the increase of solution time.In addition,the flow stress was positively correlated with the change of solid solution temperature,strain rate and solid solution timeBased on the continuum theory,the initial yield strength model and the unified viscoplastic constitutive model of 7075 aluminum alloy were constructed considering the influence of different solid solution parameters.Genetic algorithm was used to optimize the model parameters,and data of different solid solution temperature,solid solution time and strain rate were used to verify the accuracy of model parameters.The optimized constitutive model was applied to the prediction and analysis of the initial yield strength of sheet metal,which had good prediction ability and accuracy.Based on the constitutive model established in this paper,the hot forming behavior of 7075 aluminum alloy was predicted and analyzed.The VUMAT subroutines of different types of element were developed,the accuracy and reliability of the subroutines were verified by the uniaxial tensile simulation of a single element.The thermal deformation behavior of7075 aluminum alloy was accurately described by the finite element simulation of uniaxial tensile experiment.The isothermal drawing simulation of the cylindrical part without flange was carried out,the stress field,strain field and thickness distribution of the cylindrical part were analyzed.The simulation results of different solid solution parameters are compared and analyzed to prove the correctness and applicability of the constitutive model.