Low-cycle fatigue behavior of powder metallurgy 6061 aluminum alloy reinforced with submicron-scale Al2O3 particles

This paper presents the cyclic strain-controlled response of 6061 aluminum alloy reinforced with submicron-scale alumina particles, processed by powder metallurgy and consolidated by hot extrusion. Reinforcement volume fractions of 10% and 20% were investigated. Low-cycle fatigue tests were conducted under fully reversed total strain at a fixed strain rate using smooth specimens loaded along the extrusion axis. Microstructural examination revealed nonuniform spatial distribution of the reinforcing particles in both composites. At small applied strain amplitudes, as-extruded AA6061/Al2O3/10p and AA6061/Al2O3/20p composites displayed cyclic hardening under tension and softening under compression. The cyclic deformation stabilized rapidly in both composites and produced symmetric stress-strain hysteresis loops at higher strain amplitudes. The evolution of the Bauschinger effect at small strain amplitudes was rationalized based on constrained cyclic deformation imposed by the distribution of particle clusters. The stabilized cyclic stress vs. plastic strain curves for both composites showed power-law strain hardening behavior with a higher hardening rate exhibited by the higher reinforcement composite. The strain-life data were adequately modeled using the Coffin-Manson and Basquin relationships. No clear improvement was observed in the strain-controlled fatigue life data of the current composites when compared to a similar composite reinforced with an order of magnitude larger average particle-size.