抄録
Fatigue crack propagation tests with compact type (CT) specimens were carried out using three kinds of cast aluminum alloys designated AC4CH, AC1B and AC7A, which were subjected to hot isostatic pressing (HIP) treatment to reduce microshrinkage. Although the HIP-treated AC4CH showed a significant improvement of high-cycle fatigue strength under a rotating bending load, the crack propagation rate was the highest and the crack propagation threshold was the lowest among the materials included with a conventionally produced AC4CH. Since AC4CH has a eutectic microstructure, and since many fine eutectic silicon particles exist, fatigue cracks propagate easily along the eutectic part of the microstructure. The difference in crack propagation behavior represented by da/dN-ΔK relationship was well evaluated in terms of ΔKeff. Microshrinkage was found to cause a considerable rough fracture surface and secondary cracks, and appeared to conduce the crack closure.
