Numerical Simulation Study On Mg And Its Alloys Dring ECAP Based On Smoothed Particle Hydrodynamics Method

In recent years,scholars are dedicated to the study of improving the strength of magnesium and its alloys and their deformability at room temperature at home and abroad.Through the strong plastic deformation produced by fine grain strengthening is the most effective way to improve the comprehensive performance of magnesium alloy at room temperature.However,it is always a difficult problem in the field of research that how can the magnesium alloy produce a strong plastic deformation without cracking in equal channel angular pressing(ECAP)at room temperature.ECAP package process is a new ECAP technology which can effectively solve the the cracking problem of pure magnesium in ECAP deformation process at room temperature,but the process are influenced by many factors and the machining process within the mold is closed,demanding of the help of the computer simulation technology to reflect the deformation of the workpiece.Predicting the damage degree of the workpiece accurately is a necessary condition of numerical simulation,but it is difficult to realize the dynamic damage evolution process in the simulation method at this stage.Based on the meshless smoothed particle hydrodynamics(SPH)computational method,this paper has studied the dynamic deformation and crack propagation of magnesium and magnesium alloy in ECAP.The main research work and conclusions are as follows:First of all,based on the lucubration on SPH method,this paper write a calculation program for magnesium and magnesium alloy material on the deformation characteristics according to the SPH method of elastic-plastic mechanics.After verifying the correctness of the calculation procedures by the calculation of a classical example,the simulation study of AZ31 magnesium alloy under 200? ECAP deformation process is conducted and the results are consistent with the finite element software,laying a solid foundation for the establish of the damage prediction procedure based on SPH method.On the basis of the established procedures above,a calculator program with damage prediction for the dynamic damage evolution of material is conducted based on the SPH method.According to the simulation research of damage evolution process of pure magnesium in different extrusion speed in ECAP at the room temperature,this program can accurately simulate the damage evolution process of the pure magnesium.The research show that the ductile brittle transition is occurred at the high rate of deformation in pure magnesium,the formation of bundles of high strain rate converge to the shear plane in the sample gradually before the macro crack initiation and disappear in the crack to fracture;the pure magnesium presents a lamellar cracking in low deformation rate,the uniformity of plastic deformation strain rate distribution is improved,the crack relieves of the expansion of high strain concentration trend,uniform strain rate region hinders the crack propagation,the evolution process is cyclical.Finally,using the calculation program of SPH method with damage prediction,the simulation study of deformation process of pure magnesium intwo kinds of coating material in ECAP at room temperature is conducted,verifying the practicability of the program.The study shows that in the same extrusion conditions,lamellar cracking appears in the combined workpiece with the 2024 Aluminum Alloy wrapped;whereas the internal specimens of pure magnesium is complete and the uniformity is improved obviously in the extrusion process with the industrial pure iron covered.All this provide a reference for the application of the SPH method in the optimization package ECAP process.