Effect of small concentrations of gallium and lead on anodic activation of aluminium in chloride solution

Highlights: • Presence of both Ga and Pb can cause anodic activation of Al in chloride solution. • Ga without Pb has a limited effect. • Pb segregation by heat treatment starts activation locally. • Ga segregates by dealloying around segregated Pb particles forming AlGa amalgam. • Amalgam prevents repassivation and causes autocatalytic growth of activated area. - Abstract: The presents objective is to investigate the combined effect of alloyed Pb and Ga on surface segregation by heat treatment and ensuing anodic activation of aluminium in chloride solution. Model alloys containing Pb and Ga, which were heat treated in the range 300–600 °C, were characterized electrochemically in 5% NaCl solution. Annealing at 600 °C resulted in significant segregation of Pb causing limited activation, while Ga remained in solid solution. The presence 50 ppm Ga had only a small contribution to activation, while 1000 ppm Ga contributed significantly by becoming enriched at areas around Pb segregations and spreading radially by dealloying.