Environmental Friendly Composite Coating with Electroplated Nanocrystalline Zinc and Electrophoretic Paint

Combination of electroplated nanocrystalline (NC) zinc and electrophoretic coating technology was used to realize the environmentally friendly electrogalvanizing of auto parts. Nano-modification research was carried out in acidic solutions and alkaline solutions respectively. The grain size and surface morphology of electroplated NC zinc were examined by field emission scanning electron microscopy (FE-SEM). The fracture surface micrograph of composite coating was investigated by optical microscopy. Tafel curves of electroplated NC zinc in two solutions were obtained. The adhesion was tested by means of cross-cut test and neutral salt spray test was carried out on composite coating. The results showed that NC zinc was obtained in electrogalvanizing in two solutions. The corrosion current density of electroplated zinc coating decreased while the corrosion potential shifted to more positive with the increase of the current density. The time of neutral salt spray test achieved 1000 hours and the adhesion reached 5B level, which demonstrated that electroplated NC zinc bonded well with electrophoretic paint and the composite coating had excellent corrosion resisitance.