Research On Constitutive Behaviors Of C_sf/AZ91D Hot Compressed Near The Initial Melting Temperature Of Matrix

Short carbon fibers reinforced magnesium matrix composites(Csf/AZ91 D composites) have a wide application prospect in aerospace engineering and electronic communications systems owing to their high specific strength, and high dimensional stability and high wear resistance. The hot plastic forming process near the initial melting temperature of matrix alloy, in which the interfacial stress concentration and fiber breaking can be released by DRX of magnesium and trace amounts of interfacial liquid, is a new type of plastic forming method for discontinuous reinforced magnesium composites. However, the deformation behaviors of magnesium matrix composites during this process are differ from that of composites during hot forming process. In order to optimize the process parameters and conduct numerical simulation of the hot forming process near the initial melting temperature, it is vital to investigate the plastic deformation behaviors and establish the constitutive model of the Csf/AZ91 D composites during deformation near the initial melting temperature.In this paper, on the basis of isothermal compression tests of Csf/AZ91 D composites,the plastic deformation behavior of the composites compressed near the initial melting temperature was researched. According to the results of thermal simulation experiment, the dependence of flow stress on deformation temperature,deformation degree and strain rate was quantificationally analyzed. The effect of matrix alloy and fiber on strain softening in severe plastic deformation was discussed. The results provide a theoretical foundation for establishing the mechanics constitutive model of the Csf/AZ91 D composites.According to the characteristics of deformation behaviors, a viscoplastic constitutive equation based on strain compensation was proposed and established. The established constitutive equation can predict the flow stress value under the condition of different temperature, strain rate and strain with high accuracy. The characteristic of stress-strain curve especially the strain softening behavior can be revealed adequately. It provided the theoretical model for understanding the plastic deformation behaviors of these composites during severe plastic forming processing near the initial melting temperature.According to the viscoplastic constitutive equation based on strain compensation,the finite element model for describing the hot compressing process of Csf/AZ91 D near initial melting temperature was established. And the isothermal compression deformation process was numerical simulated. According to the simulated results, the distribution and the evolution of the stress field, strain field and strain rate field, of the composite billet were analyzed. The compression load-displacement curves calculated by finite element simulation agree well with that of the hot compress experiment,which indicated that the viscoplastic constitutive equation based on strain compensation can be applied in the numerical simulation and can describe the flow stress behaviors of Csf/AZ91 D composites during plastic forming process accurately.The research results provide a theoretical reference for understanding the plastic deformation behaviors and optimizing the forming process of Csf/AZ91 D composites near initial melting temperature. It probably has some common reference value for investigation on the hot plastic forming or semi-solid processing technology of the discontinuous reinforced metal matrix composites.