Double-stage hardening behavior and fracture characteristics of a heavily alloyed Al-Si piston alloy during low-cycle fatigue loading

Low-cycle fatigue tests were performed in an Al-Si piston alloy to manifest its remarkable double-stage hardening behavior and fracture characteristics. The first hardening was related to the interaction between the dislocations and the fine dispersive precipitates, and the second hardening was mainly caused by the dislocation/dislocation interaction. The fatigue fracture crack usually initiated from the large intermetallic colony which was close to the surface of specimen. The debonded Al-Si eutectic region and intermetallics provided a weak path for the crack propagation. The presence of intermetallics had a close relationship with the double-stage hardening behavior and brittle fracture characteristic at room temperature. A fatigue fracture model was comparatively put forward for the heavily alloyed Al-Si piston alloy to describe its fracture process in detail.