Surface free energies have been evaluated from Young's moduli and lattice parameter data for six Al–5Zn–0·03In alloys with varying amounts of magnesium to examine the effect of magnesium additions on the anode capacity of the basic composition. The composition containing 2%Mg exhibits a minimum in the surface free energy which accounts for the decreased tendency of this alloy to undergo passivation thus resulting in a maximum anode capacity of 2348 Ah kg−1 at 0·5 mA cm−2. Metallographic and SEM studies of typical aluminium alloys confirm that addition of 2%Mg promotes grain refinement and uniform dissolution of the alloy.
