On account of their low density and sound and energy absorption characteristics, porous materials have recently attracted a significant amount of attention. These materials demonstrate unique physical and mechanical properties, making them especially suitable for use in various industries, such as the construction, automotive and medicine industries [1
]. Metallic foams are a subset of porous materials. Because of their useful mechanical properties, they have been widely produced and evaluated [2
]. The various types of metallic foams available have been manufactured with different techniques [3
]. Magnesium, due to its high biocompatibility and lower density than other types of metallic materials, could be one of the most interesting and suitable candidates for the production of metallic foams [7
]. Different types of Mg alloy foams (with closed or open cell structures) have been manufactured with different methods, such as casting or powder metallurgy [8
]. An important subgroup of metal foams is metal matrix syntactic foam, which is composed of porous or hollow particles that are embedded in a metallic matrix [10
]. In recent years, research has mostly focused on the production and investigation of aluminum syntactic foams [11
]. Magnesium alloys have been considered for foam production due to their high specific strength. The few published studies have used cenosphere and fly ash particles as fillers [14
] to produce the syntactic foams. However, these fillers are susceptible to fracture and melt infiltration, which is amplified by a potential chemical reaction with the molten metal during casting. To decrease the proportion of fractured particles, cenospheres have been surface-coated to prevent their direct contact with molten magnesium [17
]. However, this additional surface treatment increases the complexity and manufacturing costs. Even so, a surface treatment may add additional benefits as it can be used to optimize the essential interphase between the particles and the matrix. Moreover, due to the high chemical reactivity of the metal, corrosion resistance is an important factor that must be considered for the application of Mg foams. According to [18
], the corrosion resistance of Mg syntactic foam was enhanced in comparison to pure Mg due to the incorporation of filler particles. This was explained by observing changes in the Mg’s microstructure and a decrease in the exposed Mg surface area due to partial coverage by inert silica particles. Conversely, particles that are permeable to a corrosive medium are likely to increase the corrosion rate due to the large internal surface area of a foam.
The aim of the present research work is to manufacture an innovative magnesium syntactic foam (MSF) using chemically inert filler particles. At ambient pressure, magnesium and carbon do not produce stable compounds at any temperature [20
]. Therefore, activated carbon (AC) with an ~2.8 mm particle size was used as a filler within an AZ91 magnesium alloy matrix. Micron-sized hollow AC particles have previously been used to produce a pure open-cell magnesium foam for bio-applications [21
]. The micron-sized activated carbon particles in [21
] were hollow spherical types that were removed after casting to produce an open-cell Mg foam. In the present research, granular and porous activated carbon particles were used instead and remained in the material to produce the magnesium syntactic foam. The research study [21
] focused predominantly on the oxidation and corrosion behavior of Mg foams. In contrast, the present study addresses microstructural analysis and mechanical properties evaluation. In this study, six samples of a novel AZ91/AC syntactic foam were successfully manufactured for the first time and subjected to microstructural (using a scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS)) and mechanical testing. Due to the high specific strength of the magnesium AZ91 alloy, this material may be of interest for structural applications.