Analysis of microstructure and mechanical behaviour during equal channel angular pressing of aluminium for FE-modelling

For planning forming processes it is important to know how the process parameters influence the properties of the material. Local properties like stiffness and strength are predictable with good accuracy. The main aim of the present work is to include also evolution of grain size in simulation processes. Therefore equal channel angular pressing (ECAP) was analyzed regarding to grain size during severe plastic deformation of a conventional Al-Mg-Si alloy (AW 6082 T651). The basic principle of the ECAP process is characterized by pressing a square-profiled sample rod through an angled press channel. Thereby a strong shear deformation is acting in the sample which leads to a grain refinement in the material. By varying the angle of the channel and the number of pressing operations different true strains can be generated in the material. In this work angles of 90° and 120° were used and the samples were pressed repeatedly up to 4 steps. Characterization of the microstructure was done by electron back scattered diffraction (EBSD) analysis. The results show a clear dependence of the grain size on true strain which is directly affected by the channel angle and number of passes. It could be observed that every deformation step leads to grain refinement. After 4 passes a minimal grain size of 700 nm was found, which is 5 % of initial grain size. The knowledge about the relationship between grain size and stress-strain state allows the development of models for a grain size prediction. To characterize the mechanical properties of the aluminium after every deformation step compression tests were applied. The resulting flow curves of every step were accumulated. This method allows to display deformation degrees up to 4,4. The work was done in the context of the SFB 692 HALS "High-strength aluminium-based lightweight materials for safety components".