Large Plastic Deformation Of The Composite Extrusion Of Finite Element Simulation Study

Ultrafine-grained materials have excellent mechanical properties, while maintaining toughness with high strength, which is one of the hot field of materials science research in recent years. Cyclic Channel Die Compression (CCDC) and the Equal-Channel Angular Pressing (ECAP) are two kinds of severe plastic deformation methods to make a higher accumulation of effectively equivalent strain deformation of the specimen to obtain ultrafine-grained materials without changing the material section. According to the characteristics, Combination of the Cyclic Channel Die Compression and Equal-Channel Angular Pressing obtains the ultrafine-grained materialsThe finite element numerical simulation techniques were used in the paper. The stress field, strain field, metal flow velocity field, squeezing pressure have been analyzed respectively in process of equal channel angular extrusion and composite extrusion. The maximum equivalent strain of the specimen processed two passes by CCDC—ECAP is 10.1 while the maximum equivalent strain of the specimen processed two passes by the single ECAP is 7.82. The equivalent strain distribution of CCDC-ECAP deformation is more uniform than that of the single ECAP deformation.The 6061 aluminum alloy annealed at 350℃for 2.5 hours was deformed two passes by ECAP and CCDC—ECAP.It was found that the the extrusion pressure of calculation is close to measured the extrusion force during two passes process.It shows that the parameters selecting of the process in simulation are more accurate, such as coefficient of friction and the extrusion speed.Three-dimensional finite element models of ECAP and CCDC-ECAP are established with three-dimensional finite element simulation software DEFORM-3D. The simulation caculations of two passes process by ECAP and CCDC-ECAP were carried out respectively. Deformation behavior of the 6061 aluminum alloy prepared f ultrafine grain by CCDC-ECAP was studied.The distribution and value of extrusion force, equivalent strain and stress, the metal flow characteristic which affect ultrafine crystal of 6061 aluminum alloy prepared by CCDC-ECAP were figured out. Reasons of appearance of flaws and cracks during deformation were analysised with the distribution of equivalent stress and strain. During the CCDC-ECAP deformation, the stress is focused on the front of workpiece and there is a larger tensile stress in deformation zone.The problems of specimen fracture in deformation were solved with annealing and reducing the friction between specimen and mold.Influences on refinement crystal grains of the aluminum alloy by two kinds of different process were researched. CCDC-ECAP process is better than ECAP in the grain refining effect, and the grain size are closed to 3μm after two passes process. At the same time improving the yield strength, CCDC-ECAP is also more effective than ECAP.A significant growth of the yield strength took place after one pass of CCDC-ECAP extrusion, the yield strength is from 86MPa to 124MPa, about 1.5-fold of an increase.. With the increase of extrusion passes, the hardness and strength tend to be upward, the yield strength increased to 245Mpa after four-pass extrusion.To sum up, CCDC-ECAP process is the more effective than ECAP process in the grain refinement and enhancement of mechanical properties.CCDC-ECAP process route will be payed more attention in the future study.