Electrodeposition of Zn-Ni-P compositionally modulated multilayer coatings: An attempt to deposit Ni-P and Zn-Ni alloys from a single bath

- A commonly used Zn-Ni electrodeposition bath was modified for single bath deposition of Ni-P/Zn-Ni CMMCs.
- At low current densities the Zn-Ni-P bath deposited Ni-P.
- At higher current densities the Zn-Ni-P bath deposited a Zn-Ni alloy with 3.2 wt% P.
- The overall Ni-P/Zn-Ni CMMC was sacrificial to the steel substrate.

The effects of bath composition and deposition variables on the electrodeposition of Zn-Ni-P alloys were studied in order to develop a single bath for deposition of Ni-P/Zn-Ni compositionally modulated multilayer coatings (CMMCs). The basis for development of the bath was a large increase in the Ni deposition rate compared to that of Zn at low deposition overpotentials combined with the impossibility of codeposition of Zn with P. EDS analysis demonstrated that the deposits obtained from the Zn-Ni-P bath at low overpotentials were practically all Ni-P, while the alloy deposited at high overpotentials was mainly Zn-Ni with around 3.2 wt% P content.

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