Abstract
Specimens of a commercial aluminium-magnesium-zinc alloy (7179-T651) have been tested in tension at low strain rates, either in air or vacuum after pre-exposure to water at 70°C, or in water at various potentials at ambient temperature. Pre-exposed specimens exhibit a reversible embrittlement, producing a decrease in the reduction in area to failure, the flow stress, and the ultimate tensile strength, in excess of that occasioned by testing in moist air. The embrittlement is attributed to hydrogen picked up from the environment and the recovery either to loss of hydrogen (particularly under vacuum) or diffusion to innocuous traps. The potentiostatically controlled low strain rate tests in water at ambient temperature reveal two regimes of embrittlement: one at cathodic potentials capable of generating hydrogen and the other at higher potentials giving rise to anodic dissolution. These processes may both occur at the free corrosion potential in this particular system. As well as confirming the occurrence of hydrogen embrittlement of such alloys in an aqueous environment, the observations are used to explain the difficulty experienced by many workers in reproducing embrittlement effects therein.
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