Fracture toughness and low cycle fatigue of 6061/A12O3p composites

This paper investigates the low cycle fatigue and fracture behavior of cast-then-hot-extruded 6061 aluminum reinforced with alumina particles. The effect of heat treatment and volume percentages of the particle (0–20%) on the axial fatigue behavior and fracture toughness was investigated. Cyclic hardening of the under-aged and the peak-aged samples was observed while cyclic softening of the over-aged specimens was recorded. Although fatigue data follow the Coffin-Manson's model, the fatigue resistance of the composites was lower than that of the matrix alloy regardless of aging and percentage of the reinforcement. Plane strain condition was marginally achieved due to insufficient sample thickness. The measured fracture toughness for these composites however was low compared with that of the matrix alloy and decreased with increasing reinforcement content. Scanning electron microscopy reveals that a crack starts at a machine defect and propagates through or avoids a particle depending on the relative position of the crack front and the particle. Three failure modes were found for this advanced material: cleavage fracture of a particle, cohesive delamination between matrix and particle and void coalescence in the matrix.