Investigation into the texture evolution and deformation induced material properties in the aluminum extrusion processes

Abstract

During the plastic deformation produced in the metal forming processes such as extrusion, forging and deep drawing, the crystalline lattice in the metal rotates toward one or more stable (preferred) orientations, establishing a deformation texture. The formation of this deformation texture strongly influences the mechanical properties of the product, and material anisotropy is observed from the deformation texture macroscopically. The macroscopic mechanical properties of the polycrystalline materials are the consequences of the properties of individual grains. They depend on the distribution of the orientations of the grains in the aggregate. In order to explain the mechanical response of polycrystalline materials, it is necessary to take into account the polycrystalline structure of the metal, the plastic slips on the slip systems of grains, the crystallographic lattice rotations, and the formation of textures and their evolution during the entire deformation process. During the extrusion process, metal is forced from an enclosed cavity through a die orifice by a compressive force applied by a ram. Due to the extreme plastic deformation that takes place during extrusion, the extruded profiles have strong deformation textures that produce highly anisotropic properties. However, conventional finite element analysis had not been considered the texture evolution due to the grain rotation during plastic deformation. In order to predict the texture evolution in metal forming processes, finite element models should be integrated with crystal plasticity models. Texture evolution is calculated for the entire workpiece and is updated and coupled with the finite element model during simulation. This coupled model, however, requires a great amount of computation power and is not applicable for a complicated forming process. In this thesis, the decoupled method in which the rigid-plastic finite element method is incorporated with the rate-independent crystal plasticity mo...