Aluminium based coatings for optimum sacrificial protection of high strength steel

Abstract

Sacrificial coatings, consisting of aluminium particles suspended in an inorganic chromate/phosphate binder, were investigated as possible alternatives to electrodeposited cadmium. Coatings with a range of compositions were produced by adding more active zinc or Al/Mg particles to adjust their open circuit potentials. Electrochemical measurements were carried out to study the corrosion behaviour of each coating and its ability to sacrificially protect a high strength steel substrate. Slow strain rate tests were used to assess the risk of hydrogen re-embrittlement caused to the steel by coating corrosion. A coating containing 3%Zn was shown to have the best combination of properties, with the lowest re-embrittlement risk and a good level of sacrificial protection.

Keywords:

• Aluminium based
• Sacrificial coating
• Hydrogen re-embrittlement
• Cadmium replacement

The work described in this paper was supported by Airbus UK.