Researches On Numerical Simulation In ECAP-FE Deformation Process Of ZK60 Magnesium Alloy

Because of special properties,magnesium alloy has been praised as "the most promising new material",which has became the focus of scholars.However,due to the few slip systems in the hexagonal crystal structure,the plastic forming ability of magnesium alloy is poor.Although large plastic deformation process has been affirmed in the mechanism of fine crystal reinforcing,there are still some defects such as small deformation,limited grain refinement and complicated process and so on,which have been limited the large-scale use of magnesium alloy severely.In fine crystal reinforcing,ECAP(Equal Channel Angular Pressing)process has been changed from structure of die,extrusion path and extrusion pass and other factors transition to form a new process together with other deformation ways to improve the degree of fine grain.Composite forming process is considered a more effective method compared with the traditional large deformation technology,which to overcome the shortcomings of traditional technology provides a new way of thinking.ECAP(Equal Channel Angular Pressing-Forward Extrusion)in this paper is a new large plastic deformation process,that is to say that the equal channel angular extrusion channels connected with the same cross-sectional dimension of forward extrusion so as to achieve grain refinement and improve the mechanical properties.Firstly,the composite die structure was designed according to the forming principle of ECAP-FE process,and the equivalent strain of new ECAP-FE process was compared with that of the traditional ECAP and FE processes by using the DEFORMTM-3D software.The results show that the new process has the advantages of strain accumulation;Then the DEFORM software was used to simulate the stress,strain and microstructure of ZK60 magnesium alloy during the ECAP-FE forming process on the basis of reasonable pre-processing module.The forming characteristics and field distribution of ECAP-FE were studied,and even the refinement effect of the new technology on the microstructure was predicted.These works laid a solid theoretical foundation for the development of research experiments.Finally,according to the single factor method,several sets of finite element models were created with different transition distance,die angle,extrusion ratio,extrusion temperature and friction factor.Equivalent strain,load and equivalent strain nonuniformity coefficient are taken as the standard to measure the influence of die structure and forming process parameters on ECAP-FE deformation.The simulation results show that the load and equivalent strain increase with the grow of the mode angle or the extrusion ratio,and the compression ratio can reduce the strain nonuniformity.However,the increase of transition distance could delay the time of the load change and have little effect on the load and equivalent strain.Moreover,the load and equivalent strain increase with the grow of friction factor when the friction factor increases from 0.4 to 0.6,which indicated that the larger friction is not conductive to the uniformity of the strain distribution.