Analysis of Aluminum-Based Metal Matrix Composite Reinforced with SiC Particles Studied by Scanning Electron Microscopy

The necessity for high-performance, low-cost materials for different engineering applications has led researchers worldwide to develop new materials and composites. Among the composites, metal matrix composites (MMCs) appear as a new family of materials with high mechanical performance. Among the available metals are Al, Mg, Ti, Cu, Ni, Fe, etc.; however, Al and Mg have major usage in the production of MMCs [1]. Aluminum-based composites are considered the most promising structural materials due to their corrosion resistance, wear resistance, specific modulus and weight for automobile and aerospace applications [1]. These properties can be improved by modifying the volume fraction, type, and size of the reinforcement particles. Nonetheless, for this type of composites, there are some difficulties such as particle distribution, wettability and chemical reaction between the reinforcement and the matrix. For MMCs manufacturing there are two principal methods: solid-state processing (powder metallurgy and mechanical alloying) and liquid-state processing (casting and stir casting). Additionally, novel techniques such as molecular mixing, friction stir processing and sandwich technique have been used [2]. Aluminum-based composites are reinforced with ceramic particles of oxides, carbides, nitrides and borides, among others [3]. Further, reinforcements with small size have had special attraction due to the properties they can provide; however, their dispersion into a metallic matrix is more difficult. For this reason, Isaza et al. [4] developed a technique that uses a polymer for the pre-dispersion of the reinforcements before being processed with the metallic matrix, which was used in this study. For manufacturing, 0.5 and 1 wt.% silicon carbide (SiC) particles were added to a solution composed of 4 wt.% low-density commercial polyvinyl alcohol (PVA) dissolved in distilled water. This mixture was magnetically stirred and cured in a Petri dish. Then, one composite sheet of PVA-SiC particles was alternately stacked with two aluminum sheets. Finally, the stacks were hot compacted. The present study uses field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDS) in order to identify the immersed nanoparticles into the metallic matrix and some chemical interactions between the constituents. Figure 1 shows SEM images of SiC reinforcements, where a high variation in their size and morphology can be observed. Additionally, it is possible to observe particles with very sharp areas. These characteristics improve the interaction between the reinforcement and the metal matrix, i.e., improve the mechanical anchorage, which would increase the mechanical response of the aluminum reinforced with SiC particles. Figure 2 shows SEM images for aluminum reinforced with SiC particles (0.5 and 1 wt.%) manufactured by the sandwich technique, where it is possible to observe the diffusion zone between the aluminum sheets. During the hot compaction process (polymeric sheet and metal sheets), the polymer is thermally degraded allowing the aluminum diffusion, therefore the SiC particles remain in this zone (diffusion zone). In addition, it is possible to observe that the particles are well dispersed and immersed into the aluminum matrix, which shows the effectiveness of the technique to improve the dispersion conditions of reinforcements in metallic matrices. Finally, Figure 3 shows a compositional mapping by EDS of the aluminum reinforced with SiC particles, where it is possible to observe that the diffusion zone contains aluminum, silicon and some carbon, which come from the metallic matrix and the reinforcement, respectively. However, the oxygen element also appears, which is likely to be in the form of aluminum oxide and to have been generated during the thermal degradation of the PVA [4]. According to the obtained electron microscopy results, the SiC reinforced metal matrix composite is promising for engineering applications where a high strength-to-weight ratio is required. a) SEM images of SiC particles. SEM image of aluminum reinforced with SiC particles. a) 0.5 wt.% and b) 1 wt.% SiC. EDS images of aluminum reinforced with SiC particles.