Research On Equal Channel Angular Pressing Of ZK60Magnesium Alloy

Equal channel angular pressing (ECAP) is an advanced technique based on the theory of severe plastic deformation (SPD) which to producing bulk ultrafine-grained materials (UFG). With its special advantages, the scientists have made a lot of research about this technology. With the development of the cars’lightweight and high performance, the using of lightweight materials is in urgent demand. At present, the magnesium alloy as the structural components, with the advantage of light density, high strength and rigidity, has been used in automotive and aerospace field. Therefore, it is important to study the magnesium alloy’s grain refinement processed by ECAP and explore active approach of improving the mechanical properties and formability, thus to push the application of magnesium alloy.The research object of this paper is ZK60magnesium alloy which has the highest strength. The new ECAP technology is explored via finite element (FE) simulation and experimental method. The research results provide useful guidance for the future successful incorporation of the ECAP process into commercial manufacturing and applying operations. The contents and results of this paper are generally shown as following:(1) The sound3D rigid-plastic FE model of the ECAP process is established under the DEFORM-3D platform by solving several key modeling techniques such as geometrical and material models of ZK60, meshing and boundary conditions.(2) Based on the FE models, the law of forming loads, equivalent stress and strain during the ECAP process is revealed. And the effects of multi-parameters, such as die angle, pressing temperature, friction factor, pressing speed and passes are explored. Furthermore, the ZK60FE models with channel diameters fromφ6-40mm are built. Through these simulations, the distributions of the load, equivalent strain and the nonuniformity of deformation with the increase of diameter are analyzed in detail. The simulation results provide a theory basis for the ECAP experiments. The main conclusion of the simulations shows that: the ECAP of ZK60should be conducted under the die with the inner angle Φ=90°, T=250℃, a lower pressing speed, route Bc, more passes and in good lubrication. And the deformation of the specimen with a small size is larger and more uniform than that with a large size.(3) Do the ECAP experiments of ZK60with different state of as-cast and after heat treatment. The results show that, the deformation of ZK60specimen after heat treatment is better and the grain refinement is more obvious. Thus, doing heat treatment is the necessary primise for the ECAP of ZK60specimen.(4) The grain refinement of ZK60alloy is discussed after pressing under different temperature (T=180,200,250,300℃). The ZK60specimen will craze when pressing under the temperature below200℃. The grain distribution is uniform and grain refinement is better when pressing at T=250℃.(5) The specimens of ZK60alloy are subjected to4-passes ECAP. The results show that, with the increase of passes, the grain refinement is getting better, the number of fine grain with small size is larger, and the grain distribution is more uniform. The grain size from～110μm refined to～11μm after1pass, and refined to～5μm after4passes. Thus ECAP process is an effective method of grain refinement.(6) The pressing results of ZK60specimens with different diameters of φ10mm and φ30mm after2-passes in two ECAP die-sets with different channel diameters is comparatively studied, the grain size respectively refined to～6μm and～8μm. The grain refinement ofφ10mm is bigger than that of φ30mm.(7) The grain refinement at different regions on the cross section of ZK60with two different diameters after1and2passes are compared. The grain refinement and the equivalent strain of simulation have positive correlation. And the change of vicker hardness and the deformation of the specimen is consistant. So the grain refinement and the vicker hardness of experiment can be explained by the equivalent strain of simulation.(8) The shape of ZK60specimen from FE simulation is the same with the experimental result. The grain refinement is consistant with the equivalent strain of simulation. Thus the FE models are verified by the ECAP experiments and the simulation results are reliable.