Electrodeposition of Zn–Ni coatings as Cd replacement for corrosion protection of high strength steel

Electrodeposition of Zn–Ni coatings performed in acidic baths are not suitable for high strength steels due to their high susceptibility to hydrogen embrittlement.In this work, Zn–Ni coatings were deposited on a high strength steel (4340) upon stirring conditions from an alkaline bath. A complete characterisation of the coatings (corrosion, morphology and composition) has been accomplished, correlating the electrodeposition conditions with these features. The best protective properties of the grown coatings were achieved for the alloys with a single phase structure of γ-Ni5Zn21 and a denser morphology. Additionally, the hydrogen content incorporated is lower than even cadmium-coated 4340 steel which has undergone a postbaking dehydrogenation treatment.

Research highlights
► Electrodeposition of Zn–Ni coatings from an alkaline bath on a high strength steel.
► Complete characterisation of the coatings (corrosion, morphology and composition).
► Correlation of the electrodeposition conditions with the properties of the film.
► Similar corrosion resistance than Zn–Ni coatings deposited from acidic baths.
► Lower hydrogen content incorporated than for a post baked cadmium-coated steel.