Characterisation and modelling of the biaxial material behaviour of twin-roll-cast, hot rolled and annealed AZ31 sheets

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Mostly ecological aspects are the driving force for the development of innovative lightweight solutions nowadays. Especially the use of light metals such as magnesium is of remarkable importance. In this regard, the resource-saving and economical roll-casting of magnesium strip was developed. Due to the hexagonal lattice structure and thus reduced number of sliding systems at room temperature, the metal forming processing of roll-cast magnesium strip is difficult. Alternative deformation mechanisms as twinning, grain boundary sliding and kink banding which perform differently depending on stress-modus, temperature and deformation degree, have a decisive influence on the forming properties. It therefore requires accurate modelling and approaches to depict the realmaterial behaviour, in order to carry out a realistic technological design using numerical simulation. Standardized material models and datasets to describe anisotropy, flow locus, microstructural development and damage have reached the limits of their validity,with the consequence of inaccurate or false results in the numerical calculation. Previously developed models have been designed for continuously casted and then hot-rolled sheets of AZ31 magnesium alloy, which at present only show inadequate references to the consideration of biaxial stress states. Specifically, the biaxialcompression-compression and tension-compression stress states have been rarely studied, although this is of immense importance for modelling the flow locus. To date the deficiency of focus lies in the correlation of influencing micro-structure and coupling of the resulting mechanical properties. In this context, the consideration of inductiveheating and damage under biaxial stresses in process-relevant conditions is absent. To generate scientific added value, models regarding anisotropic material behaviour, damage and forming limit behaviour should be designed, expanded and validated for roll-cast, hot-rolled and annealed AZ31 sheet. Here, firstly uniaxial stress states will be investigated and in the subsequent phase of the project all models will be adapted to biaxial stress states and tested through a real deep drawing process with complex geometry. The result of the research project will have an increase of numerical predictioncapability and precision as outcome, in order to improve the material modelling for metal forming processes and expand the application possibilities of magnesium alloys.