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Aluminium alloys can become anodically activated by the presence of trace elements from group IIIAVA in chloride environment,as a result of enrichment of these elements at the surface during heat treatment,as characterized by pitting potential depression and high current output during anodic polarisation.This paper focuses on activation by bismuth in relation to the available information on activation by Pb.AlBi model alloys containing 20 and 100 ppm Bi were investigated by use of electrochemical polarisation,electron optical techniques and glow discharge emission spectroscopy (GDOES).In contrast to Pb,Bi gives activation by heat treatment at temperatures as low as 400℃.Activation increases with increasing annealing time and temperature.Quenching in water after annealing at 600℃ results in the formation of a thick,porous hydrated oxide of order 1 μm in thickness.This layer covers a much thinner thermally formed crystalline γ-Al2O3 oxide.While some segregated Bi particles become trapped in the hydrated layer,some remain at the thermally-formed oxide – metal interface.These segregated particles which is in contact with the metal are believed to cause activation.In situ observation of the corroding surface during potentiodynamic polarization indicated a multi-step process,involving thinning of the hydrated layer and undermining of the thermally formed oxide,probably as a result of activation by underlying segregated Bi.