Einfluss der Mikro- und Makrostruktur auf das Deformationsverhalten und die Druckfestigkeit offenzelliger, präzisionsgegossener Aluminium-Schäume

Besides the low weight, good thermal conductivity and high porosity open-cell foam structures exhibit very good mechanical damping properties. Especially the damping properties promise interesting applications, e.g. in the automotive and transportation fields. However, up to now metal foam’s material models are inaccurate. In addition, there is a missing understanding of the mechanical properties’ scatter hindering the large scale application of open-cell foams in automotive serial production. Current literature offers only limited information about the influence of the foam struts’ imperfection, cross-sectional form, and microstructure. In order to close this current research gap, the process and design parameter, and the chemical composition were systematically varied during the production of open-cell precision-cast aluminium foams. The foams were analysed in regard to their micro- und macroscopic deformation behaviour during compression test; and their microstructure and strength, as well. If foam cells are arranged stochastical there is a little influence of missing struts on the compression strength. Due to the initiation of a high number of micro cracks notched struts lead to a smooth stress plateau and a slight decrease of the compression strength. The strength of open-cell, bending-dominated foams is significantly increased by a triangular cross-sectional form of the struts due to its higher bending stiffness. The use of a ductile basic material for highly porous foams leads to a continuously increase of their stress plateau during compression due to strain hardening. In this case, the compression strength is mainly determined by the foam’s relative density and can be calculated with the Gibson-Ashby-model. Due to the supporting effect of collapsed struts the compression strength of less porous, ductile foams differ from the prediction of the Gibson-Ashby-model. With decreased porosity the energy absorption efficiency is decreased. At a strut diameter of < 260 µm in precision-cast metal foams there is one grain per strut; secondary phases are located between the dendrite arms and around the dendrite leading to an increased number of phases next the struts’ surface. By an increase of the amount of eutectic phases the overall phases’ distribution is more homogeneous leading to a less oscillating stress plateau. Polygonal, spiky phases lead to a more distinctive peak stress and a discontinuous stress plateau progression. If secondary phases are rounded, e. g. by alloying, there is a continuous transition between the linear-elastic section to a smoother stress plateau. Small, plate-shaped secondary phases increase the density-normalised compression strength accompanied by a slight increase of the command variable’s scatter. The present work contributes to the understanding of the systematic influence of the (micro-)structure on the deformation and compression strength of open-cell, precision-cast foams. With the aid of the developed models the compression strength of these foams can be calculated precisely