Fatigue Performance of Pre-corroded 6xxx Aluminum Alloy Laser Beam Welds with Dissimilar Heat Treatment

The role of existing corrosion damage on the fatigue performance of 6156 AA laser beam welds in T3 state, with additional post weld heat treatment T8, has been assessed. The welds were subjected to salt fog environment for 720hours and then metallographically examined to characterize corrosion behaviour. The corrosion results demonstrate that T3/T8 treatment provides high corrosion susceptibility in the weld area, where localized damage in the form of large pits prevails. Fatigue performance of corroded samples is drastically degraded by the presence of corrosion pits which act as stress raisers and accelerate crack initiation in the corroded samples. Fatigue cracks initiate at the root of corrosion pits on the large specimen surfaces in the weld metal area and propagate in through thickness direction. The obtained results have been compared to results from 6156 welds with T4 treatment in as welded conditions.