2.2.3 Galvanised Steel
- Galvanisation involves the application of a zinc-iron alloy layer to steel in order to protect it from corrosion.
- The deformation and adhesion properties of the zinc layer are determined by the size of the zinc crystallites. Large zinc crystallites undergo less deformation because stress peaks develop at the grain boundaries when substrates are deformed. This results in a rapid loss of adhesion.
- Two main processes are distinguished:
- Hot dip galvanisation: The covering of the steel components with a solid, metallic zinc coating by dipping the pretreated steel components in a melt of liquid zinc. This causes relatively large zinc crystallites to form.
- Electrolytic galvanisation: The workpieces are immersed in a zinc electrolyte, not a melt. The deposited zinc layers are made up of mainly smaller crystallites.
- In general, electrolytically galvanised steel surfaces have a more uniform stress distribution and hence offer higher adhesion strength.