Development of a generalised understanding of environmentally-assisted degradation of magnesium-aluminium alloys

Common factors affecting the susceptibility of Mg-Al alloys to creep, corrosion and stress corrosion cracking are the influences of the concentration and morphology of the beta phase. The influences of the beta phase on the various degradation modes are interrelated and may have opposing consequences on durability. This paper provides an overview of the influences of the beta phase on the mechanisms for degradation of Mg-Al alloys in extreme environments. Preliminary results aimed at evaluating the role of the beta phase in the corrosion behaviour of high-purity Mg-Al alloys in 3.5% NaCl solution using electrochemical noise analysis are given. The results show a general increase in corrosion resistance with increasing total Al concentration. This is rationalised in terms of the effect of Al-enrichment of the surface film. The implications of the results on alloy development are discussed.