Corrosion Behavior of Nanocrystalline Bulk Al-Mg-Based Alloys Available to Purchase

The corrosion behavior of a series of nanocrystalline Al-Mg alloys has been investigated and compared to that of conventional aluminum alloy 5083 (AA5083 [UNS A95083]). Experimental results showed that the nanostructured Al-Mg alloys did not exhibit significantly superior polarization behavior in terms of passive current density or breakdown potential, when compared to microstructured conventional AA5083. The open-circuit potentials for the nanocrystalline alloys were typically lower than that of the conventionally processed alloy, although this feature is most likely a reflection of a high Mg concentration in these alloys rather than smaller grain size. The pits observed on nano alloy surfaces were smaller than those present on the conventional alloy AA5083. Scanning electron microscopic (SEM) observation of corroded surfaces revealed that corrosion attack for both the conventionally processed and the nanocrystalline alloys initiated at inclusions. In the case of the nanostructured materials, these inclusions were smaller and less numerous than those noted on the conventional alloy. Results of ASTM G-67 intergranular corrosion tests revealed that the nanocrystalline alloys were susceptible to intergranular corrosion while the conventional AA5083 was resistant.