Polypyrrole film on 55% Al–Zn-coated steel for corrosion prevention

► A conducting polypyrrole (PPy) layer was anodically formed to protect Al–Zn alloy coating. ► The alloy−coated steel can be passivated by the oxidative PPy layer. ► No corrosion products were observed during 60 h immersion in aqueous NaCl solution. For corrosion protection of 55% Al–Zn-coated steel, a dense polypyrrole (PPy) film is electrochemically formed on 55% Al–Zn-coated steel in an acidic tartrate solution under constant current control. The film potentially consists of an inner layer of aluminium and/or zinc oxide and an outer PPy layer doped with tartrate anions. The PPy layer can maintain passivation of 55% Al–Zn-coated steel in a 3.5 wt.% NaCl aqueous solution and protected the steel for several hours. The doping of molybdate anions into the PPy–tartrate film greatly improved the film’s protective properties.