## 2 Materials and Methods  
### Foams Production Method and Material Composition  
The production of closed cell aluminum foams using the powder compact melting method involves several steps, including powder preparation and mixing, compaction, melting, and foaming. A sketch of the production method is reported in Figure 1. The manufacturing technique summarized here is described with major details in a previous work [20]. In fact, many parameters affect the foaming process: composition of the powders, size, and shape of the stabilizer's particles, powder mixing and conditions, temperature, and pressure during powder compaction, temperature of the oven, heating rate of the foam precursor, foaming time, atmosphere and pressure on the melt, and, finally, cooling rate to room temperature. Foam precursors have been prepared by using Al powder (purity 99.5%) with an average diameter of 45 \(\upmu\)m, SiC particles with an average diameter of 37 \(\upmu\)m and TiH\({}_{2}\) particles with an average diameter of 5 \(\upmu\)m. Four set of samples have been produced by mixing together at room temperature different amounts of TiH\({}_{2}\) (0.2, 0.4 and 0.6 wt %) and SiC (2.8 and 6.0 wt %), as detailed in Table 1. For each composition, 5 samples have been produced in order to check the repeatability of the process and, consequently, the morphological and mechanical properties; average properties have been reported. In the first step, aluminum (Al) powders are mixed with a blowing agent (Titanium Hydride) and a stabilizing agent (Silicon Carbide) to create a powder mixture [21] in a rotating device whose distribution is as uniform as possible. This mixture is then compacted with a uniaxial pressure system under a load equal to 12 t. At the end of the compaction step, a manageable solid precursor is obtained. The precursor is then placed inside a copper crucible which must be oxidized in an oven at 700 \({}^{\circ}\)C before using it. After inserting the precursor in the crucible, the whole system is heated in a furnace up to a temperature above the melting point of aluminum, typically around 700-750 \({}^{\circ}\)C, depending also on the composition of the alloys. At this temperature, after a few minutes, the aluminum powders melt while the blowing agent releases gas (H\({}_{2}\)), creating closed cells within the molten aluminum matrix. In the case of Al powders, the oven temperature was set at 700 \({}^{\circ}\)C, not much higher than the Al melting point (660 \({}^{\circ}\)C). This choice was driven by the melt viscosity being too low at higher temperatures. The precursors were heated to 700 \({}^{\circ}\)C in about 120 s in order to avoid an excessive gas dispersion before foaming. During the foaming process, the pressure inside the closed cells increases, causing the surrounding aluminum to expand and form the foam structure. The foaming process is carefully controlled from the top side of the oven monitoring the growth of the foam. The dwell time in the oven is critical for achieving the desired cell size, distribution, and density of the foam. Typically this time is in the range 4-6 min, depending on the mass of the employed powders. With shorter dwell time the growth of the foam is limited as well as porosity size, while with excessive longer times, coalescence between bubbles is the main problem, with the opposite problem that porosity size becomes excessive and consequently compromises the mechanical properties. When the foaming process is completed, the closed cell aluminum foam is cooled down in water. Four compositions have been investigated in the present study, derived from earlier studies [14; 19; 20], focused on the detailed definition of the manufacturing process, as detailed in Table 1.