Ab initio and thermodynamic modelling of alloying effects on activity of sacrificial aluminium anodes

This work summarizes the experimental literature to date on Al-alloy sacrificial anodes and shows that the presence of Sn as an alloying element in solid solution form consistently debases the alloy corrosion potential. This study then assesses the lattice expander theory, which states that lattice-expanding dopants can be used to increase Sn solubility in Al and thereby reduce passivation. The thermodynamic effects on Sn solubility of lattice expanders (Ga, Mg, Zr, In and Bi) are predicted with ab-initio methods. Our results support lattice expander theory although we demonstrate that Sn solubility can decrease by alloying with even large dopants if they form compounds with Sn.

Research highlights
► Effect of alloying on the corrosion activity of sacrificial Al anodes.
► Sn in solid solution form is a key alloying element for activation of Al anodes.
► Ternary additions that increase Sn solubility decrease the potential of Al alloys.
► Elements bigger than Al expand the Al lattice and allow more Sn to dissolve in Al.
► Large ternary dopants can reduce Sn’s solubility in Al if they form compounds with Sn.