Pitting-induced hydrogen embrittlement of magnesium–aluminium alloy

In this study, the pitting corrosion susceptibility and its role on the hydrogen embrittlement behaviour of AZ80 magnesium alloy were studied using slow strain rate testing (SSRT), electrochemical technique and immersion test method. The electrochemical and immersion tests in chloride-containing solution revealed severe pitting corrosion in the alloy. The SSRT results of the alloy under continuously-exposed conditions in chloride-containing solution and in distilled water showed that the mechanical properties of the alloy deteriorated considerably in both the solutions. Pre-exposure of the alloy in distilled water did not show any considerable change in the mechanical properties of the alloy, however in chloride-containing solution a significant loss in the mechanical properties was noticed. Cleavage facets were observed in the vicinity of the localized attacked region of the alloy pre-exposed in chloride-containing solution. Interestingly, desiccating the pre-exposed (in chloride-containing solution) samples reduced the loss in the mechanical properties, which could be attributed to reversible hydrogen. Thus, the study suggests that pitting corrosion facilitates hydrogen entry into the alloy and causes hydrogen embrittlement.

► Pitting susceptibility of Mg–Al alloy plays a crucial role in the EAC of the alloy.
► Pits act as an initiator for SCC in Mg–Al alloy.
► Pitting corrosion induces hydrogen entry into Mg–Al alloy leading to HE.