Advanced manufacturing of metal matrix syntactic foams

Advanced manufacturing of metal matrix syntactic foams (MSFs) is the focal point of the present thesis. In particular, the manufacturing of low-cost materials for potential commercialisation. The thesis investigates a novel pre-compaction process for the counter-gravity infiltration technique. This manufacturing step allows the casting of expanded perlite-aluminium syntactic foam with densities ranging from 0.74 to 1.06 g/cm³, without the changing of raw materials. The way in which the infiltration casting process influences the material properties of MSF is further analysed in contrast to the stir casting technique. Finally, the influences of filler particles and the metal matrix on the manufacturing and properties of MSF are compared. The choice of manufacturing technique influences the morphology of the foam. While infiltration casting yields open-cell morphologies, stir casting yields closed-cell MSF. The closed-cell morphology significantly improves strength. The open-cell morphology is mainly caused by low particle wettability and occurs because of a lack of infiltration of inter-particle voids. The wettability is influenced by the outer structure of the filler particles. Particles with an outer shell have an increased contact surface, which lowers the wettability between ceramic particles and melt. The tested porous particles (expanded glass and expanded perlite) have low mechanical strength and do not contribute significantly to the strength of the MSFs. Their benefit is in having lower prices than other established filler materials, such as synthetic hollow spheres. They are thus very attractive for future large-scale processes. This work further examines the influence of the matrix material on the manufacturing and the properties of the MSFs. Aluminium exhibits high specific strength and is affordable but shows limitations if exposed to loads at high temperatures. Zinc has the benefit of lower processing costs arising from a lower melting point but lacks in terms of achievable densities and is slightly more expensive than aluminium. This thesis introduces novel manufacturing techniques and contributes to the broader understanding of lightweight MSFs.