Codeposition Behavior of Zn-Ni-SiO2 Composite Platings

Akira TAKAHASHI, Yasuhiko MIYOSHI, Takashi HADA
1993 Journal of The Surface Finishing Society of Japan  
Zn-based composite plated steel sheets are expected to exhibit better corrosion resistance than zinc-or zinc-alloyplated steel due to the existence of dispersed particles. It is of importance, therefore, to clarify the codeposition mechanism of the dispersed particles in order to control the plating structure, and thereby control the corrosion resistance. A study was conducted on the electrodeposition behavior of Zn-Ni-SiO2 composite plated steel sheets that were electroplated from an
more » ... d from an electrolyte containing Zn ion, Ni ion and SiO2 colloid. It was found that the SiO2 content of the plated layers increased rapidly with an increase in the SiO 2 concentration in the bath, showing that Guglielmi's two-step codeposition mechanism did not hold in this case. The cross-sectional structure of the plating layer was studied by grow discharge spectrometry (GDS) and transmission electron spectroscopy (TEM). It was found that Zn-7.4wt%Ni-1.6vol%SiO2 composite plating had a double-layered structure : an under layer consisting mainly of Zn-Ni alloy and an outer layer of segregated SiO2 thin film. Zn-12.lwt %Ni-20.5vol %SiO2 composite plating, on the other hand, had a laminar structure, consisting of aggregated layers of SiO 2 and Zn-Ni alloy, and Zn-Ni alloy layers. It was concluded that these codeposition behaviors depended on the peculiar properties of SiO2, which adsorbs Ni ions in the bath selectively, and agglomerates at the cathode.
doi:10.4139/sfj.44.977 fatcat:iduzsz2bdveqthak7p5hh7ms4e