Theoretical Study of the Influence of Microalloying on Sensitization of AA5083 and Moderation of Sensitization of a Model Al-Mg-Mn Alloy via Sr Additions

The calculated effect of a range of quaternary alloying additions to aluminum alloy (AA)5083 (Al-4.4Mg-0.5Mn [UNS A95083]) was investigated. Attention was given to the influence of composition on the volume fraction of β-phase (Mg2Al3), and the possible formation of any additional phases (which we term γ-phase herein). Alloying additions of silver, cerium, copper, lithium, neodymium, nickel, scandium, silicon, strontium, yttrium, zinc, and zirconium were studied in hypothetical additions of 0.1 wt% and 0.5 wt%, revealing that there is potential to modify the fraction of β-phase, and hence sensitization, in AA5083. Calculations indicated strontium to be the most effective addition in decreasing β-phase fraction during thermal exposure (sensitization); therefore, the influence of Sr additions were studied empirically via production of custom Al-Mg-Mn alloys. Sensitization was investigated via the nitric acid mass loss test (NAMLT), revealing that mass loss from intergranular corrosion decreased by more than 60% from the addition of 0.08 wt% Sr; however, further Sr addition (up to 0.35 wt%) subsequently led to a small decrease in mass loss. Analysis of intentionally fractured surfaces of sensitized alloys confirmed a substantial decrease in β-phase on grain boundaries due to Sr additions.