The effects of the addition of silica binder during preform preparation on the development of interfacial compounds in squeeze-cast SiC p /6061 Al composites (containing silicon carbides with particle sizes of 85, 30 and 14 μm) were examined using energy dispersive spectroscopy (EDS) X-ray mapping, scanning electron microscopy (SEM) fractography and optical microscopy (OM). Various interfacial compounds, Al 2 O 3 , MgO and MgAl 2 O 4 , were observed. The effects of the various interfacial compounds on the SEM fractography and mechanical properties of the composites were investigated and a mechanism was suggested. The micromechanism of crack initiation, crack propagation and final fracture was discussed using SEM fractography and OM observations.