Influence of frequency and waveform on corrosion fatigue crack propagation in the 2024-T351 aluminium alloy in the S–L orientation

This study was undertaken in order to identify the domains of possible synergistic effects between corrosion and fatigue damage during crack growth in aluminium alloys. In this aim the 2024-T351 aluminium copper alloy was selected and tested in the S–L orientation. The effects of load frequency and waveform have been investigated at a load ratio R = 0.7 in a 3.5% NaCl solution and compared to data obtained in air and distilled water. In saline solution, a fatigue crack growth enhancement associated with transitions in the da/dN curve is observed at high frequencies under sinusoidal signals, while low frequencies provide results comparable with those obtained in air. It is furthermore shown that this behaviour is primarily controlled by the rising time (RT), i.e. the duration of the rising load part of a cycle, and not by the period. A competition between passivation of the crack tip and hydrogen embrittlement caused by localized anodic dissolution may account for the frequency effect observed in this study.