Comparison of the plastic deformation and failure of A359/SiC and 6061-T6/Al2O3 metal matrix composites under dynamic tension

A comparison is presented of the dynamic plastic deformation and tensile failure of two metal-matrix composites (one with a cast alloy matrix and the other with a wrought alloy matrix). The two composites are ceramic particle reinforced aluminum alloys: F3S.20S (A359 aluminum alloy reinforced by 20% SiC particles) and W6A20A (6061-T6 aluminum alloy reinforced by 20% Al2O3 particles). The corresponding unreinforced matrix alloys were also examined. The effects of strain rate on the tensile responses of these composites were determined using the tension Kolsky bar. The microstructures and fracture surfaces of the specimens of each composite were examined using SEM and optical microscopy. The experimental results show that the flow stresses of both composites are higher than that of their matrix alloys, whereas the composite fracture strains are lower. The fracture strains of the W6A20A composite and the 6061-T6 monolithic matrix alloy were much higher than those of the F3S20S composite and the A359 monolithic matrix alloy. Both the W6A20A composite and 6061-T6 monolithic matrix alloy behaved in a ductile manner with necking prior to fracture, while both the F3S.20S composite and A359 monolithic matrix alloy behaved in a brittle manner with no necking prior to fracture. Microscopic examination revealed tensile failure of the A359 matrix alloy and its composite to be controlled by the microcracking of Si network, which formed in the interdendritic silicon rich region, whereas failure of the 6061-T6 based composite is controlled by cracking of reinforcement particles. (C) 2004 Elsevier B.V All rights reserved.