Intergranular Corrosion and Stress Corrosion Cracking of Sensitised AA5182

Abstract

AA5182 (Al-4.5 wt% Mg) can become susceptible to intergranular corrosion (IGC) with time at moderately elevated service temperatures owing to precipitation of Mg-rich β-phase at grain boundaries, which can lead to stress corrosion cracking (SCC). The IGC and SCC susceptibility of AA5182 was found to depend strongly on sensitisation heat treatments. AFM and TEM studies demonstrated that the degree of precipitation and thus susceptibility to attack for a boundary can be related to its crystallographic misorientation. Low angle boundaries (<20°) are most resistant to attack as they do not show β-phase precipitation. However, higher angle boundaries show highly variable precipitation and corrosion susceptibility: critical factors are the grain boundary plane and precipitate/matrix crystallographic relationship.

Influence of Mg Content on the Sensitization and Corrosion of Al-xMg(-Mn) Alloys

“…Consequently, these calculations can be used as a general guide for DoS interpretations, which in the future would be even more beneficial if the proportion of grain boundary β phase could be isolated from microstructural characterization. The temperature dependence of DoS has been shown (for individual alloy compositions) in prior works, 22,25,30 which have revealed a lower DoS value for higher temperatures, consistent with Figure 9, when adjusting for time. 31 conclusIons v In this work we present the simultaneous influence of Mg content on the hardness, corrosion, and DoS of Al-xMg-0.5Mn alloys, where x varies from 3.36 wt% to 8.85 wt%.…”

Influence of annealing temperature on sensitisation behaviour and corrosion properties of an Al‐6.8 wt% Mg alloy

“…Correlation between the mass loss in NAML test (Table ) and SCC susceptibility (Fig. ) is concurrent with the other reports indicating that the IGC susceptible specimens with the mass loss below 40 mg/cm 2 might not be prone towards SCC.…”

“…d) due to the large specific volume difference between β‐(Al 3 Mg 2 ) phase and Al matrix . There are no other reports on the faceting transition in the Al–Mg system, but the observations of ‘ribbon’ or ‘saw‐tooth’ morphology of the grain boundary precipitation might be an indication of the faceting. The presence of the faceted grain boundaries could further facilitate crack propagation contributing to SCC susceptibility.…”

“…Precipitation of the β‐(Al 3 Mg 2 ) phase appears to be more advanced in deformed than in recrystallised microstructure of AA 5083 alloy‐type materials that underwent similar sensitisation treatment. Grain boundary crystallography has an influence on nucleation and growth as well as morphology of β‐(Al 3 Mg 2 ) phase .…”

Effect of magnesium and titanium on the cathodic behaviour of aluminium in nitric acid

“…marine environment, magnesium undergoes passivation due to surface pH increase thanks to initial Mg(OH) 2 formation. Further, when the Mg content exceeds about 3 wt.%, Al–Mg alloys are particularly susceptible to intergranular corrosion and stress corrosion cracking . This has been directly related with the tendency to precipitate in the grain boundaries of Mg 5 Al 8 , which is much more anodic than the aluminium matrix.…”