Abstract
The fatigue behaviour of friction stir processed (FSPed) cast aluminium alloy, AC4CH-T6 was investigated. Fully reversed axial fatigue tests have been performed using as-cast, FSPed and post heat treated (PHTed) specimens. The FSPed specimens exhibited lower fatigue strength in high stress region, but higher fatigue limit than the as-cast specimens. Casting defects were eliminated by FSP, resulting in higher fatigue limit. However, the crack growth rates of the FSPed specimens were faster than the as-cast ones due softening of the material by heat input during FSP. This led to the lower fatigue strength of the FSPed specimens in high stress region. Post heat treatment could recover the hardness, but it was detrimental to crack initiation resistance. The effects of FSP and PHT were discussed based on the microstructural consideration.
