Fatigue failure investigation of pre-corroded and laser-welded Al-Cu-Mg-Ag Alloy with different temper condition

Abstract

The fatigue failure mechanisms of pre-corroded, laser beam welded Al-Cu-Mg-Ag alloy in different temper conditions (T3,T8) have been investigated. Aging influences the corrosion behavior of laser welds. In the T3 temper, corrosion attack is in the form of pitting in the weld area, while in the T8 temper corrosion is in the form of intergranular corrosion in the base metal. In the latter case corrosion is attributed to the presence of grain boundary precipitates in the base metal. Corrosion degrades the fatigue behaviour of 2139 welds. The degradation is equal for both the T 3 and T 8 tempers and for the corrosion exposure selected in this study corresponds to a 52% reduction in fatigue limit. In both cases fatigue crack initiation is associated with corrosion pits. In the T3 temper, the fatigue crack initiation site is at the weld metal/HAZ interface, while for the T 8 temper the initiation site is at the base metal. Fatigue crack initiation in uncorroded 2139 welds occurs at the weld toe at the root side, the weld reinforcement playing a principal role as stress concentration site. The fatigue crack propagates through the PMZ and the weld metal in all cases. Fatigue crack initiation in the corroded 2139 welds occurs exclusively at corrosion pits which act as stress raisers.