The fatigue characteristics of Al-6Si-4Cu alloy casting solution-treated at 807K, which is approximately 17K higher than the ternary eutectic temperature, were investigated. The influence of pore configuration on fatigue fracture was studied by X-ray computer tomography in three dimensions. The fatigue limit of the specimen solution-treated at 807K decreased approximately by 18%, compared to alloys solution-treated with the standard T6 conditions. This is thought to be due to the eutectic dissolution resulting from solution-treatment above the eutectic point. Significant difference was observed in fatigue strength between alloys with and without high-temperature solution treatment in the high cycle region, whereas the difference was negligible in the low cycle region. When the volume fraction of pore exceeded 0.2% and/or macro-pores existed near the casting surface, fatigue life was found to shorten in both the high and low cycle regions. The negative effects of high-temperature solution treatment appeared to be dominant over the positive effects for fatigue.
