Corrosion and stress corrosion behaviour of an Mg-Li-AI alloy in presence of inhibitors in aqueous environments

Magnesium-lithium alloys are potential candidates for use in aerospace-applications as they are of low density and have high stiffness. However, owing to their susceptibility to corrosion and stress corrosion in chloride environments, they have limited applications. The aim of the present work is to study the effect of two corrosion inhibitors namely potassium chromate and n-butylamine on the corrosion and stress corrosion behaviour of a Mg-11Li-1Al alloy. Polarisation studies were carried out for examining the corrosion behaviour and the fracture mechanics approach is used to assess stress corrosion behaviour. It has been observed that the addition of n-butylamine to distilled water, and potassium chromate to NaCl solution has improved the corrosion resistance. Crack growth studies have revealed that a 20% increase in K1scc occurs with the addition of 0·05 N n-butylamine to distilled water; this inhibitor has no effect, however, in NaCl solution. Similarly, there is no significant improvement with 0·05% addition of potassium chromate to distilled water, whereas potassium chromate addition to 0·5% NaCl solution brought about an increase of 28% in K1scc. These results are interpreted in terms of the electrochemical reactions involved during corrosion of the alloy.