Al-Based Metal Foams (AMF) as Permanent Cores in Casting: State-of-the-Art and Future Perspectives

Metal foams are extremely interesting due to their low density, high specific stiffness, and impact energy/vibration absorption ability. The use of metal foams as permanent cores in casting can be an opportunity to improve the properties of cast components and to simplify the technological processes (e.g., no need for core removal/treatment/recycling). The present review, besides a brief introduction on commercially available metal foams and their main characteristics, reports and compares the research works and patents related to the use of metal foams as permanent cores in casting, with particular attention to foam characteristics (e.g., presence/absence of surface skin, porosity and density, and liquid to foam volume ratio), casting parameters (e.g., pressure, the temperature of poured material, die material, and cooling rate), core–shell bonding and strategies for its improvement (foam surface treatments/coatings). The main issues that limit the application of metal foams as permanent cores in casting (e.g., poor core–shell bonding and poor foam resistance to casting conditions) are finally discussed together with possible solutions for their overcoming. Finally, characterization techniques, suitable for the investigation of foams, casting objects, and the core–shell bonding are summarized and compared in order to facilitate the selection and optimization of the more suitable ones.