Corrosion behaviour of zinc-nickel alloy coatings electrodeposited in additive free chloride baths

Corrosion behaviour of nanocrystalline Zn-Ni alloy coatings (with 3 to 18 at-%Ni) electrodeposited on steel substrate from additive free chloride baths by DC plating has been investigated by measurement of open circuit potential with time and neutral salt spray test. The alloy coatings containing up to 16 at-%Ni exhibited an increase in resistance to the appearance of white and red rust with increasing Ni content. The resistance to the appearance of white rust and ability to protect the underlying steel substrate decreased with further increasing Ni content. This has been considered to be due to reduced passivating ability of the alloy coating with a significant rise in the grain size above 50 nm.