Corrosion Fatigue Behavior of a Duplex Aluminum Bronze Alloy

Fully reversed axial fatigue tests of a duplex aluminum bronze alloy (CDA958, ABS4) have been performed in laboratory air and in 0.5N NaCl solution as functions of applied anodic and cathodic currents, α grain size, and test frequency. It has been shown that free corrosion of the alloy during cyclic stressing results in a 25 to 30% decrease in endurance limit at 10⁷ cycles and that there is a tendency away from transgranular crack initiation in air toward crack initiation between contiguous α grains. Increasing corrosion rates by applying anodic currents further reduces corrosion resistance and increases the tendency toward interphase crack initiation. Cathodic currents, on the other hand improve fatigue resistance in chloride solutions, but even relatively large applied currents do not completely restore the fatigue properties observed in air. Altering α gram size by more than an order of magnitude does not appreciably affect corrosion fatigue resistance. Decreasing test frequency, on the other hand, shows a marked reduction in corrosion fatigue resistance. Results to date indicate that preferential corrosion of aluminum rich regions in the alloy leads to early crack initiation, and that the corrosion resistance of the alloy is the primary variable which affects corrosion fatigue resistance.