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

如今，主要是生态方面推动了创新轻量级解决方案的发展。特别是使用轻金属，如镁，是非常重要的。为此，开发了资源节约型、经济型镁带连铸技术。由于铸轧镁条的六边形晶格结构，从而减少了室温下滑动系统的数量，使铸轧镁条的金属成形加工变得困难。孪晶、晶界滑动和扭结带等变形机制对合金的成形性能有决定性影响，这些变形机制的表现随应力模态、温度和变形程度的不同而不同。因此，需要精确的建模和方法来描述真实的材料行为，以便使用数值模拟进行现实的技术设计。用于描述材料各向异性、流动轨迹、微观结构发育和损伤的标准化材料模型和数据集已经达到了其有效性的极限，导致数值计算结果不准确或错误。先前开发的模型是针对AZ31镁合金的连铸和热轧板设计的，目前只考虑了双轴应力状态。具体来说，双轴压缩-压缩和拉-压缩应力状态很少被研究，尽管这对流动轨迹的建模非常重要。迄今为止，重点的不足在于影响微观结构的相关性和由此产生的力学性能的耦合性。在这种情况下，没有考虑在与工艺相关的条件下双轴应力下的感应加热和损伤。为了产生科学的附加值，应该设计、扩展和验证铸轧、热轧和退火AZ31板的各向异性材料行为、损伤和成形极限行为模型。在这里，首先将研究单轴应力状态，在项目的后续阶段，所有模型将适应双轴应力状态，并通过具有复杂几何形状的真实深拉深工艺进行测试。研究结果将提高数值预测能力和精度，以改进金属成形过程的材料建模，扩大镁合金的应用可能性。

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.