## 6 Discussion  
The study of metal foams has received increasing interest in recent years due to their unique properties, such as high strength-to-weight ratio, excellent energy absorption capacity, and acoustic insulation. Metal foams have potential applications in several industries, including aerospace, automotive, and biomedical. Therefore, it is useful to understand their physical properties and how they can be modified to enhance their performance. The compression test is a standard method utilized to assess the mechanical properties of foam. In this work, the foams have been compressed up to a specific strain level, and the force required to achieve that strain has been measured. The compression test provides insights into the foam's compressive strength and energy absorption capacity. The experimental analysis performed in this work is based primarily on closed-cell aluminum foams. The composition of such materials has been changed in order to get four different types of samples. After the compression tests, the strain energy was evaluated, and sample 2 showed the highest strain energy per unit volume. The analysis of morphological properties, such as area, circularity, and equivalent diameter, can provide a better understanding of the foam's structure and porosity, parameters which can be manipulated to enhance the foam's properties for specific applications, both structural and functional. In this work, the foams have been analyzed from a morphological point of view: physical properties of the foams, such as area, circularity, and equivalent diameter, were determined using image analysis software. This analysis was conducted on all four samples and the main results are discussed in the following. From the comparison of Figures 9-14, it has been found that the geometrical features (area, circularity, and equivalent diameter) of the porosity critically depend, at first glance, on the TiH\({}_{2}\) content. In general, foams manufactured with 0.2% TiH\({}_{2}\) show pores of smaller size and homogeneous size in comparison with the ones produced with 0.4% and  
Figure 14: Comparison of distribution of equivalent diameter for different amount of SiC. 0.6% of TiH\({}_{2}\) (Figure 9). With increasing TiH\({}_{2}\) content the bubble's size raises too and a greater dispersion of the porosity size has been evidenced. The consequence of increasing SiC content is shown in Figure 10, where the stabilizing effect of the ceramic particles is particularly evident in the smallest range of area (0-0.05 mm\({}^{2}\)). Dealing with circularity, it has been found that the highest values are achieved with the lower content of TiH\({}_{2}\) (Figure 11) and with the higher content of SiC (Figure 12). As concerns the equivalent diameter, it is reflected in the situation of the area illustrated in Figures 9 and 10. The effect of the addition of TiH\({}_{2}\) increases porosity size and consequently the equivalent diameter (Figure 13) while the stabilizing effect of SiC addition has the greatest impact on the smaller porosity size (Figure 14). The distribution of particles on the walls between adjacent porosities contribute to the stabilization of the foam structure, reducing drainage of molten metal and increasing the resistance to metal flow. In this way, thinning of the walls is prevented, wall strength is enhanced, and, in general, mechanical strength is increased. The analysis of the absorbed energy per unit of volume (specific energy) with a different amount of TiH\({}_{2}\) (Figure 7) evidenced that absorbed energy increases from 0.2% to 0.4% TiH\({}_{2}\) and decreases from 0.4% to 0.6% of TiH\({}_{2}\). The main reason for that can be ascribed to the contribution due to the lower plateau stress and higher strain found with increasing content of TiH\({}_{2}\). The specific energy is the area below the curve \(\sigma\)-\(\epsilon\), so the opposite contribution due to stress and strain are evident from these results.