• Kamm, P.; Neu, T.; Garcia-Moreno, F.; Banhart, J.: Nucleation and growth of gas bubbles in AlSi8Mg4 foam investigated by X-ray tomoscopy. Acta Materialia 206 (2021), p. 116583/1-16

10.1016/j.actamat.2020.116583
Open Access Version

Abstract:
Initiation and growth of metal foam is a complex and dynamical process, which is intrinsically three- dimensional and time-dependent. Tomoscopy –or time-resolved tomography–allows us to follow the nu- cleation and growth of gas bubbles in AlSi8Mg4 alloy in real time during foaming. The location, size and shape of individual bubbles was determined in steps of 1 s with spatial resolutions of a few μm. Moreover, the constituents responsible for gas evolution, namely Al-Mg phases and TiH 2 particles, were identified in the series of 3D images. Automated quantitative image analysis of bubbles and gas-generated phases including their spatial correlations allowed us to break down the foaming process into two distinct steps, a first homogenous one driven by adsorbed gases and first melting microstructural components and a second attributed to the melting of the alloy and subsequent foam growth driven by hydrogen released from TiH 2 particles. The results of the study indicate that standard AlSi8Mg4 foam can be improved by tailoring the properties of the Al-Mg constituent powder.