Multi length-scale characterisation of microstructure/geometry interactions for tailoring properties of open-cell Al alloy foams

泡沫金属是能量吸收和轻质建筑应用的有前途的候选者。在μm到cm长度尺度上，相、支柱和细胞是分层结构元素。因此，基础材料及其微观结构，例如第二相的形状和量，以及支柱和单元的几何形状、拓扑结构和尺寸，决定了机械性能。在这里，尺寸效应在凝固和机械性能方面都起着重要作用。控制这些变量是发展具有良好定义的准静态和动态性能的金属泡沫的基本条件。我们的目标是在考虑冶金和几何方面的情况下修改分级结构元素及其相互作用。我们的科学目标是了解作用于不同长度尺度的机制，这些层次结构元素之间如何相互作用，以及它们对机械性能的影响，以开放的多孔铝合金泡沫为例。通过调整合金成分、变质元素的含量和热处理，可以调整mm尺寸支柱的显微组织。在这里，我们将考虑沉淀物和枝晶臂距离的尺寸和几何形状的影响。支柱的几何形状、长度和厚度将变化以改变支柱的刚度，并且泡沫的泡孔拓扑结构将通过引入封闭泡孔壁或附加支柱来改变。金属泡沫将主要通过块状成型铸造工艺生产，基于泡沫聚氨酯或增材制造的蜡模型。此外，通过增材制造在内部生产的金属开孔泡沫以及市售的烧结开孔和闭孔泡沫将被纳入调查。通过各种高分辨率的二维和三维成像方法，如SR-μCT、SEM或TEM，将在泡沫、泡孔和支柱的长度尺度上观察微观结构和机械诱导损伤的发展。研究结果将有助于我们更好地了解是否以及在何种程度上可以将大块铝合金的冶金和机械知识转移到mm尺寸的支柱和泡沫本身。结果将总结在一个模型中描述的微观结构/性能关系的开孔金属泡沫的应用适应调制的变形行为。

Metal foams are promising candidates for energy absorption and light weight construction applications. On the μm- to the cm-length-scale, phases, struts and cells are hierarchical structural elements. Thus, the base material and its microstructure, e.g. the shape and amount of second phases, as well as geometry, topology and size of struts and cells, determine the mechanical properties. Here, size effects play an important role, both regarding solidification and mechanical properties. Control of these variables is the basic condition for the development of a metal foam with well defined quasi-static and dynamic properties We aim at modifying the hierarchical structural elements and their interactions under consideration of metallurgical and geometrical aspects. Our scientific goal is the understanding of the mechanisms acting on the different length-scales, how these ineract between the hierarchical structural elements, and their influence on the mechanical properties, on the example of open porous Al-alloy foams. The microstructure of the mm-sized struts will be adjusted by adaptation of the alloy composition, the content of modifying elements and through heat treatments. Here, we will consider size and geometry effects both of precipitates and of the dendrite arm distance. The geometry, length and thickness of the struts will be varied to change the stiffness of the struts, and the cell topology of the foams will be modified by introduction of closed cell walls or additional struts. The metal foams will mainly be produced by the block moulding casting process, on the basis of foamed polyurethane or additive-manufactured wax models. Additionally, metallic open-cell foams, produced in-house by additive manufacturing, as well as commercially available sintered open-cell and closed-cell foams, will be included in the investigations. The microstructure and the development of mechanically induced damage will be observed on the length-scales of the foams, cells and struts, by a variety of high resolution 2D and 3D imaging methods, such as SR-μCT, SEM or TEM. The results will help us better understand whether and to what extent metallurgical and mechanistic knowledge of bulk Al-alloys can be transferred to the mm-sized struts and the foams themselves. The results will be summarised in a model describing the microstructure/property-relationship of open-cell metal foams for an application-adapted modulation of the deformation behaviour.