Effect of MnO 2 addition on the microstructure and properties of high-volume fraction SiC p /Al composites fabricated by pressureless melt infiltration

High-volume fraction silicon carbide particles reinforced aluminum matrix composites (SiCp/Al) with low coefficient of thermal expansion (CTE) and high thermal conductivity (TC) were fabricated by infiltrating Al-Si-Mg alloy in air atmosphere without pressure into porous SiC preforms doped with different manganese dioxide (MnO₂) content in order to investigate the effectiveness of MnO₂ as infiltration aid. The effect of MnO₂ on the infiltration time, microstructure and thermo-mechanical properties of the composite materials were studied. The volume ratio of SiC to MnO₂ was set at 100:0, 100:5, 100:10 & 100:15 respectively. Obtained results showed the effectiveness of MnO₂ as infiltration aid as the infiltration time was significantly reduced, the wetting between SiC and Al and interfacial bonding strength were considerably improved with the addition of MnO₂. Harmful and brittle aluminum carbide (Al₄C₃) was not detected at the interface of the Al alloy and SiC ceramic phase. The composites with 100:15 MnO₂ and 100:10 MnO₂ content were found to have less incubation period and infiltration time. Optimum dispersion of SiC particles in the Al alloy and better properties were obtained with 100:10 MnO₂ content composite samples. The properties are; a coefficient of thermal expansion (RT to 473 K) of 9.3 × 10⁻⁶ K⁻¹, a thermal conductivity of 200.5 W/(mK), a hardness of 145.2 HBW and a bending strength of 338.0 MPa.