The effect of variable humidity on corrosion fatigue of AA7085-T7451 with surface salt deposits

Abstract

Abstract Corrosion fatigue (CF) crack growth is quantified as a function of relative humidity (RH) using AA7085-T7451 samples with NaCl deposited to understand the effect of deliquesced surface electrolyte droplets on CF performance when humidity varies. Fracture mechanics testing holding mechanical driving forces for cracking constant and incrementally increasing humidity show that crack growth rate (da/dN) more than doubles once RH moves above 78–80% RH. When decreasing RH, some amount of drying below the efflorescence RH (ERH) and/or a sufficient time is needed to pass in order for da/dN to return to that expected for a dry crack tip. All in all, this study establishes time of crack tip wetness as an important parameter for predicting fatigue lifetimes in atmospheric conditions, a parameter that cannot be solely predicted by RH, as accelerated cracking can continue for a limited amount of time even when RH is brought below the ERH.