Hydrogen re-embrittlement of high strength steel by corrosion of cadmium and aluminium based sacrificial coatings

When high strength steels absorb hydrogen during corrosion of a sacrificial coating they can fail by a process termed hydrogen re-embrittlement. This paper compares the levels of re-embrittlement caused by coatings of electroplated cadmium and two possible alternative aluminium based coatings. Slow strain rate tests were performed on coated tensile specimens exposed to 3.5%NaCl solution or pre-exposed to a coastal marine atmosphere. Permeation experiments were used to measure the absorption of hydrogen over a range of potentials, including those typical of the corroding sacrificial coatings. The severity of re-embrittlement was shown to be controlled not only by the corrosion potential of the coating but also by its barrier properties, which can limit hydrogen uptake by the steel substrate.