INFLUENCE OF MATRIX STRENGTH ON REINFORCEMENT FRACTURE AND DUCTILITY IN AL-AL2O3 COMPOSITES

Two Al alloys (2014 and 6061) reinforced with 15 vol.% Al2O3 particula tes were tested in the naturally aged and peak-aged conditions to stud y the influence of matrix strength on the mechanisms controlling the t ensile ductility of these composites. Periodic measurements of the deg radation of elastic properties during deformation, as well as quantita tive metallography, indicated that the dominant failure mechanism was progressive fracture of the particulates during deformation. The proba bility of particulate fracture increased with the reinforcement size, and elongated particulates oriented in the loading direction were more prone to fail than small, equiaxed ones. It was also observed that th e particulate fracture rate increased with the matrix strength and tha t the naturally aged composites were able to withstand more damage pri or to failure than those artificially aged at high temperature. When a critical volume fraction of broken reinforcements was reached at a gi ven section of the specimen, matrix failure led to specimen fracture b y a ductile mechanism of shear failure or void nucleation and growth f rom inclusions or precipitates in the matrix.