Research On Hot Deformation Behavior And Processing Map 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 mechanical 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 thermal processing maps under different true strains.In this paper,20vol.%T300 short carbon fiber reinforced AZ91D magnesium alloy.Based on the flow stress curve of high temperature plastic deformation and quantitative metallographic experimental results of microstructure,the influence of deformation temperature,strain rate and strain on the flow stress and micro-deformation mechanism of C_sf/AZ91D composites was analyzed,and the fiber volume was established.The high-temperature deformation mechanical constitutive model of C_sf/AZ91D composites with a fraction of 20%and its thermal processing map at true strain 0.2,0.4,0.6and 0.7.Based on the established thermal processing maps,the deformation characteristics and corresponding micro-deformation mechanisms of the composites under different high-temperature deformation conditions were analyzed.By comparing with the thermal processing maps of the magnesium alloy AZ91D at true strains of 0.4 and 0.6,the mechanism of high temperature deformation and micro-deformation of carbon fiber pair C_sf/AZ91D was revealed.This establishes the plastic deformation limit conditions of C_sf/AZ91D composite materials,and provides theoretical guidance for the rational development of the thermal processing technology of C_sf/AZ91D composites.The main findings are as follows: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 the composites 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 addition of short carbon fiber promoted the DRX of the matrix magnesium alloy and refined the recrystallized grain structure.The energy dissipation efficiency factors of C_sf/AZ91D composites were higher than 30%in the deformation temperature range of about 415⁴60℃and the strain rate of about 10^-3-10^-2s^-1.This region was mainly concentrated in the high-temperature and low-strain rate regions.Also known as the dynamic recrystallization zone,which is the right-lower zone of the thermal processing map,this is the optimum range of forming parameters for hot working of C_sf/AZ91D composites.There are two types of instability in the deformation of the rheologically destabilizing zone:one is the local cracking of the interface between the matrix and the fiber,the other is the adiabatic shear band formed by the inhomogeneous dynamic recrystallization fine grain zone,and the increase in the amount of strain in the region of rheological instability tends to increase.