Microstructure Evolution Behavior And Numerical Simulation Of C_sf/AZ91D Composites During High Temperature Deformation

Short carbon fibers reinforced magnesium matrix composites(C_sf/AZ91D)have attracted increasing attention due to their lightweight,excellent mechanical property,good isotropic property and the ability for secondary processing.Compared to traditional light alloy,however,the application of C_sf/AZ91D composites is still limited,to extend their application in lightweight structure,proper secondary processing is required to improve their microstructure and property.Due to the hexagonal close-packed crystal structure of magnesium alloy and the addition of reinforcement,C_sf/AZ91D composites can hardly be deformed at ambient temperature.Therefore,in this paper,the plastic deformation behavior of C_sf/AZ91D composites under high temperature was investigated,and focus on the research for the microstructure evolution of matrix alloy during high temperature plastic deformation.In this paper,the 20 vol.% T300 short carbon fiber reinforced AZ91 D magnesium alloy,namely.C_sf/AZ91D composites,were prepared by a vacuum assisted liquid metal infiltration method.The influence of deformation temperature,strain rate and strain on the plastic deformation behavior and microstructure evolution of matrix alloy was investigated based on the obtained flow stress curves and quantitative metallographic experiment results.The effect of carbon fiber on the behavior of flow stress and dynamic recrystallization（DRX）during high temperature deformation was revealed through comparing with magnesium alloy AZ91 D.A DRX constitutive model of C_sf/AZ91D composites during high temperature deformation was developed.The finite element numerical simulation was carried out based on the constitutive model.The simulation results were in good agreement with the experimental ones,which provide a theoretical basis for the reasonable plastic deformation parameters and predicting the microstructure property of C_sf/AZ91D composites.The main conclusions were as follow.The flow stress of C_sf/AZ91D composites during high temperature compression decreased with the increase of deformation temperature and the decrease of the strain rate.At a given deform temperature and strain rate,the flow stress of C_sf/AZ91D composites increased rapidly to the peak value with the increase of strain,then decreased significantly to the steady value.The strain softening degree of thecomposites was higher than that of the magnesium alloy.An obvious DRX was found during the high temperature compression deformation process of C_sf/AZ91D composites,the grain size after deformation got refine substantially.The average recrystallized grain size and critical strain for DRX increased with the increase of deformation temperature or the decrease of strain rate.The volume fraction of the DRX grain increased with the increase of strain in a nonlinear form,which exhibit a rapid-slow-stable mode.The addition of short carbon fiber promoted the DRX of the matrix magnesium alloy,reduced the critical strain for DRX and refined the recrystallized grain structure.The DRX constitutive models of C_sf/AZ91D composites,which included the kinetics model and the average grain size prediction model,were developed based on the flow stress curves and the results of quantitative metallographic analysis.The calculated value of both two models could match the experimental ones on the whole,which provided a theoretical model for quantitative analysis and prediction of microstructure during high temperature deformation of C_sf/AZ91D composites.Combined with the nonlinear finite element software,the developed models were written into the subroutine by Fortran to simulate the procession of high temperature compression of C_sf/AZ91D composites.The distribution and evolution for DRX structure of the composites under different deformation conditions was studied.The simulated results,which included the average grain size and the volume fraction of recrystallized grains,were in good agreement with the experimental ones,thereby validating the accuracy of the developed models.