The free expansion of different aluminium-foam precursor materials has been measured by a image-based three dimensional expandometer based on an alternating 90 deg-rotating plate introduced inside an infrared heating furnace and an imaging system. The foaming behaviour of uni-axial compressed tablets, symmetrical-shaped extruded profiles, non-symmetrical-shaped extruded profiles and a thixocasted precursor material has been compared. Dissimilar expansion in the early foaming stages has been observed for the different studied materials. These differences have been explained in terms of the different bonding of the metal grains in different directions associated to phenomena such as the anisotropic processing pressure, shear forces and relative movements of these particles. The time-uncoupled expansion in the different directions drives to an elevated cell anisotropy in the early-stage of foaming, giving as a result a still remaining anisotropy at high expansions and causing, additionally, part of the cell defects in the final cellular structure. In order to improve the aluminium foam structure it is important to suppress this uncoupled expansion changing the foaming conditions, pressing steps or using a foaming agent with an onset temperature next to the melting point of the base alloy.
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