Silicon dissolution and interfacial characteristics in Si/Al composites fabricated by gas pressure infiltration

The silicon dissolution and interfacial characteristics of Si/Al composites were investigated by microstructure analysis and thermodynamic calculation. A new method of gas pressure infiltration was proposed to fabricate the Si/Al composites with near-net shape. The interfacial characteristics were examined using SEM, TEM, EDS and X-ray Diffraction, especially, silicon particles with reaction products were extracted through the electrochemical etching. The results show that some Si particles have been dissolved and a lot of crusts filled with Al matrix are left. The SiO2 layer in Si/Al composites has three functions: to enhance the interfacial strength by interfacial reactions between Si particles and Al matrix, to serve as barriers to prevent the Si particles from being dissolved by molten Al alloy, and to join Si particles to form Si preform. However, the barriers will not perform these functions when they are damaged. The SiO2 barriers are consumed by molten Al alloy, and the major phase in the interfacial reaction products between the SiO2 barriers and the molten Al is Al2O3, while MgAl2O4 is the minor phase. Furthermore, the reaction of an equation “4Al (L) + 3SiO2 (S) = 2Al2O3 (S) + 3Si (S)”is the dominant interfacial reaction in the Si/Al composites, which is different from the dominant reaction in SiC/Al composites.