FRACTURE-BEHAVIOR OF PRESSURE DIE-CAST ALUMINUM-GRAPHITE COMPOSITES

Fracture toughness values of pressure die-cast Al-7Si-3 Mg-5 graphite composites were measured and found to be in the range 8-10 MPa m(1/2). Detailed microstructure of the composite and the fractured surfaces w ere examined. Defects such as clusters, agglomerations and segregation of graphite particles, play a dominant role in accelerating the fract ure process. In addition, the acicular silicon phase present in the ma trix and the casting defects, such as gas and shrinkage porosities, al so initiated and accelerated the crack, thus lowering the fracture tou ghness of the composites.