Pore connectivity of aluminium foams: effect of production parameters

This work studies the effect of some production parameters on the pore connectivity grade (i.e., the open-cell content associated cracks and missing cell walls) of aluminium foams produced via powder metallurgy route. Two types of precursors, extruded and hot uniaxially compressed, were used to create a varied group of Al–Si and Al–Si-Mg alloy-based foams in a wide porosity range. The cellular structure and defects were characterized by gas pycnometry and X-ray tomography. The analysis performed points to a high pore connectivity in all foam specimens, despite these materials are classified as closed celled due to their appearance, and a significant dependence on all the parameters varied. These dependences and the related mechanisms are discussed in the paper in terms of (i) the dissimilar foam evolution at initial stages (effect of precursor processing technique), (ii) the solidification shrinkage of each alloy (effect of composition) and (iii) the cell wall thinning (effect of foam porosity and local drainage). In addition, it has been observed that the interconnections are preferably located in the central parts of the samples, thus suggesting the possible effect of the cooling conditions on defect generation.