Production of Al-Cu-Fe metallic foams without foaming agents or space holders

This investigation presents a study on the intrinsic formation of Al68Cu20Fe12 alloy foams, i.e. without the need of foaming agents or space holders. This alloy was slowly solidified in the furnace crucible, producing a multiphase microstructure, mainly composed by the λ-Al13Fe4, I-icosahedral, θ-Al2Cu and ω-Al7Cu2Fe phases. Several heat treatments were carried out to a number of as-cast alloy samples in order to produce foams with porosities above 60%. The microstructure, thermal properties, pore morphology and porosity were characterized by means of SEM, DTA, Image analyzer and Archimedes principle, respectively. The highest amount of macro porosity of up to 65% and a density of 1.5 g/cm3 in the treated sample were found at 900 °C for 360 min. At this temperature, a highly porous structure formed mainly by the λ-Al13Fe4, I-icosahedral and ω-Al7Cu2Fe phase was obtained. The proposed mechanism for the intrinsic porosity formation is based on the high amount of liquid phase generated by the melting of the Cu-rich phases and the peritectic reaction. The reaction between the λ-Al13Fe4 and the liquid phases formed the highly dense ω-Al7Cu2Fe and I-icosahedral phases. Thus, the space that is left behind caused the highly porous structure in this material.