Abstract
Fracture toughness, S-N curve and fatigue crack propagation behavior in melt-forged aluminum casting alloys such as AC4C-T6 and AC8A-T6 were investigated at room temperature and 423K, and were compared with these in a commercial 6061-T6 wrought alloy. The static or dynamic fracture toughness, JIC or Jd for AC4C-T6 and AC8A-T6 alloys was lower than that for a 6061-T6 alloy. The S-N curves for AC4C-T6 and AC8A-T6 alloys were situated lower than that for a 6061-T6 alloy. This was because of a pre-existed surface flaw effect by coarse Si particles in the casting alloys. The fatigue crack propagation in AC4C-T6 and AC8A-T6 was unstable in a high stress intensity range, because a large number of fracture-initiation sites such as Si and compounds were distributed in these alloys comparing with a 6061-T6 alloy. On the contrary, the value of ΔKth increased in a lower stress intensity range because Si particles and compounds acted as obstacles against crack propagation.
