Insight into classifications and manufacturing processes of metallic foams: A review

Metal foam (MF) is a cellular structure made up of solid metal with a substantial volume of gas-filled pores or hollow reinforcements of the space holder. The porosity of the foam can be isolated, interconnected, or hybrid. These kinds of ultra-light materials typically have 60% to 90% porosity. Based on the porosity content MFs are classified into open, closed, partially open, and syntactic foams. However, foam made from non-flammable metal continues to be non-flammable and can be recycled as base metal. It has a similar coefficient of thermal expansion, while thermal conductivity is drastically reduced. MF has vast applications due to its superior properties, including excellent specific strength, high specific stiffness, extraordinary energy absorption capacity, good vibration damping, and premium sound attenuation capability, especially in foams with isolated or hybrid porosity. At the same time, foams with interconnected porosity have superior heat transfer capability, reasonable electromagnetic shielding, infiltration, and catalytic capability. Despite the current development, several challenges still prevent metallic foams from being commonly utilised in various industrial sectors. These challenges include high manufacturing costs, uncertainty in measured properties, and the lack of proper testing procedures. This article summarises manufacturing routes, associated processing features, and future roadmap with the present state of the art.