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1771356 
Journal Article 
EFFECT OF A FOAMING AGENT AND ITS MORPHOLOGY ON THE FOAMING BEHAVIOUR, CELL-SIZE DISTRIBUTION AND MICROSTRUCTURAL UNIFORMITY OF CLOSED-CELL ALUMINIUM FOAMS 
Kevorkijan, V; Skapin, SD; Paulin, I; Kovacec, U; Jenko, M 
2012 
1 
Materiali in Tehnologije
ISSN: 1580-2949 
46 
3 
233-238 
WOS:000305657100007 
A quantitative evaluation of the microstructure of aluminium foams and, particularly, any quantitative comparison is: a very demanding and complex issue. In this work, the cell-size distribution (CSD) was proposed as the most efficient approach for their assessment. The foams were made by the powder metallurgy (P/M) route, by applying titanium hydride and dolomite powders of five different average particle sizes as the foaming agents. The average size of the pores and the pore-size distribution were estimated by assessing optical and scanning electron micrographs of as-polished foam bars by applying the point-counting method and image-analysis software. The uniformity of the CSD in the foamed samples with closed cells was studied as a function of the particle size distribution of the foaming agents, the average particle size of the applied AlSi12 powders, the concentration of the foaming agents, the foaming temperature and the foaming time. Generally, the samples foamed with the dolomite foaming agent had a more uniform cell-size distribution and a lower average bubble size. The most uniform cell-size distribution was achieved in the foam samples foamed with the minimum amount of the mass fraction (w = 0.5 %) of dolomite powder grades, having the lowest average particle size and a narrow particle-size distribution. In contrast, in samples made from coarser and less-uniform grades of foaming agents, the cell-size distribution was broader, with a significantly higher fraction of large bubbles. Longer foaming times and higher foaming temperatures also led to foam samples with a less-uniform microstructure. Based on the experimental findings and theoretical considerations regarding aluminium-foam microstructural development, the preconditions for stable bubble growth into a homogeneous and uniform foam structure were modelled and compared with the experimentally determined values. 
aluminium foams; comparison of different foaming agents and processing parameters; microstructural characterisation; modelling of microstructural development