Hydrogen effects in the corrosion fatigue behaviour of the white zone of 7xxx series aluminium alloy welds

Abstract The environment sensitive fracture under cyclic loading of the white zone of 7017-T651 aluminium alloy has been investigated. Fracture mode transitions (intergranular/transgranular) have been observed to take place at certain crack velocities and for frequencies above 0.1 Hz they depend upon the square root of the reciprocal of the loading frequency, which is shown to be consistent with an environment enhanced crack growth rate involving hydrogen diffusion ahead of the crack tip during each cycle. For frequencies below 0.1 Hz the fatigue crack growth is found to be a time dependent rather than a cycle dependent phenomenon. Striations observed on the fatigue fracture surface indicate a discontinuous crack propagation mechanism and a model suggesting that crack initiation takes place at the region of maximum stress, ahead of an existing crack tip, facilitated by hydrogen accumulating there, has been demonstrated.