Effect of alternative aging process on the fracture and interfacial properties of particulate Al2O3-Reinforced Al (6061) metal matrix composite

The effects of different aging processes on ductility, fracture, and interfacial properties in particulate Al2O3-reinforced Al (6061) MMCs were studied. Tensile tests based on relevant ASTM standards were performed to investigate the mechanical responses of specimens under different heat-treatment conditions. SEM, field-emission SEM (FESEM), and TEM studies were carried out to correlate fracture mechanism(s) with microstructural features. Based on the experimental results, the overall effect of heat treatment on tensile properties is similar to that in the monolithic alloy; however, the rate of recovery in fracture-related properties, such as elongation to fracture, is lower in the overaged condition for the MMC samples. To explain this "low" recovery behavior of overaged MMCs, the following observations have been taken into account: (1) a shift of the materials' behavior from particle fracture to interface (or near-interface) debonding fracture, when moving from the underaged to overaged regime, and (2) more frequent observations of interfacial reaction products (spinel) on the fracture surface of overaged specimens. The presence/formation of spinel phase at the interface was recognized as the main cause of this behavior. Although spinel products mainly form during material processing, they may continue to form in the solid state as well. As a result, the surface morphology of the spinel phase in the underaged specimens is different from that in the overaged specimens. (Author)