Al-induced electroless Co/Sn bi-layered deposition and evaluation of corrosion resistance

Al-induced electroless bi-layered Co/Sn coating was fabricated on a mild steel substrate by plating the Co layer as a primer and the Sn as an outer layer. This Co/Sn bi-layer coating was prepared by using a dual bath (chloride-based electroless Co and Sn bath) with varying single-layer thickness. The growth rate of the primer and outer layers was evaluated in a temperature range of 60° to 90°C. The morphology, composition, and phase structure of the coatings were characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffractometer (XRD), respectively. The bi-layer coating showed a significant improvement in corrosion resistance in terms of a reduction in corrosion current and corrosion rate and an increase in polarization resistance compared to the single-layer coating. (author)