Effect of MnO2 addition on the microstructure and properties of high-volume fraction SiCp/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 x 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.