AC4CHアルミニウム合金鋳造材の疲労き裂伝播に及ぼす凝固組織の影響

抄録

The fatigue crack growth behavior of a Al-Si-Mg base cast aluminum alloy (AC4CH) has been investigated with special reference to the effects of solidification structure. Fatigue crack growth tests under the constant load amplitude condition have been perfbrmed using CT type specimens of systematically controlled solidification structures with such as dendrite arm spacing, size and morphology of eutectic Si particles and matrix aging conditions. The results were discussed from view points of microstructures and fracture mechanics. The da/dN-ΔK relationship reveals that refining and spherodizing of eutectic Si particles improve fatigue crack growth resistance in the high ΔK range, while the crack growth rate at the lower limit range is not influenced by morphology of the particles. Matrix aging condition influences little the near-threshold and the Paris regime fatigue crack growth. The crack growth resistance in the high ΔK range is improved by increase in ductility of matrix. It is, however, deteriorated by the coarser dendritic structure which yields the higher crack growth resistance near the threshold level.