Fatigue crack propagation of AZ61 magnesium alloy under controlled humidity and visualization of hydrogen diffusion along the crack wake

Fatigue crack propagation (FCP) tests were performed using as-received and T5-treated magnesium (Mg) alloys, AZ61, in the environmental chamber, in which the humidity was controlled from 20%R.H. up to 85%R.H. FCP rates were faster in the humid environments than in dry air after allowing for crack closure, even if the humidity was low. Hydrogen diffusion along the crack wake could be visualized by a hydrogen microprint method, and the size of diffusion area was dependent on humidity and stress concentration factor. The acceleration could be primarily attributed to hydrogen embrittlement and secondary to anodic dissolution at fatigue crack tip.