Early pore formation in aluminium foams studied by synchrotron-based microtomography and 3-D image analysis

The mechanisms behind pore formation in aluminium alloys that are in commercial use for making foam components are still not understood. It is accepted that they play a key role in the quality of the evolving pore structure. In order to shed light on early pore formation, aluminium foams in low expansion stages made by the powder-compact melting process were investigated by synchrotron-based hard X-ray microtomography and quantitative image analysis. The calculated spatial correlation functions between the gas source (TiH 2 particles) and the nucleating pores show that the location of pore formation and the spatial gas source distribution for AlSi7 and Al–Si–Cu alloys are essentially independent. Therefore, in the alloys investigated, the position of the melt formation is found to determine the pore nucleation rather than the spatial distribution of TiH 2. This behaviour explains the known positive effect on the pore structure achieved by adding copper.