Effect of electrodeposition conditions on the composition, microstructure, and corrosion resistance of Zn–Ni alloy coatings

The formation, composition, and structure of electrodeposited zinc–nickel alloys were investigated. It has been shown that both anomalous and normal codeposition of zinc and nickel can be realized by changing the bath composition and deposition conditions, with the nickel content in the resultant deposit being varied in a wide range (from 2 to 90 at.%). It has been also shown that the ammonical diphosphate electrolyte allows deposition of Zn–Ni coatings with a homogeneous phase structure (Ni5Zn21 and Ni3Zn22 intermetallides, a solid solution of Zn in Ni, or a solid solution of Ni in Ni5Zn21), whereas the weak acid chloride electrolyte produces two-phase coatings consisting of Ni5Zn21 with the admixture of polycrystalline Zn or Ni. The Zn–Ni coating with a nickel content of 19 at.% consisting of Ni5Zn21 intermetallic phase exhibits the highest corrosion resistance.