Strength and fracture toughness of interpenetrating graphite/aluminium composites produced by the indirect squeeze casting process

Graphite/aluminium composites with an interpenetrating network microstructure were produced by the indirect squeeze casting process. Porous isotropic graphite preforms with about 14.5 vol.% porosity were infiltrated either with AlSi7Ba or AlSi12. Flexural strength and fracture toughness were determined at room temperature and 300 °C before and after thermal cycling. The composites exhibit a significantly higher mechanical strength and fracture toughness than the graphite preforms. The infiltration with aluminium alloys enhances the flexural strength by a factor of two up to about 120 MPa and increases the fracture toughness from 0.94 to 1.93 MPam1/2. At 300 °C, no decrease in flexural strength of the composites is observed. Thermal cycling results in a slight reduction of the mechanical properties for graphite/AlSi7Ba composites, while graphite/AlSi12 composites show no decline in strength and toughness, respectively. The effect of aluminium composition and thermal cycling on the mechanical properties are explained by means of a crack bridging model.